Can't find GPU #96

RUST_BACKTRACE=1 cargo run --example breakout
   Compiling bevy_wgpu v0.1.0 (/home/void/tmp/bevy/crates/bevy_wgpu)
   Compiling bevy v0.1.2 (/home/void/tmp/bevy)
    Finished dev [unoptimized + debuginfo] target(s) in 6.45s
     Running `target/debug/examples/breakout`
thread 'main' panicked at 'called `Option::unwrap()` on a `None` value', crates/bevy_wgpu/src/wgpu_renderer.rs:22:23
stack backtrace:
   0: backtrace::backtrace::libunwind::trace
             at /cargo/registry/src/githubproxy.fjygbaifeng.eu.org-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/libunwind.rs:86
   1: backtrace::backtrace::trace_unsynchronized
             at /cargo/registry/src/githubproxy.fjygbaifeng.eu.org-1ecc6299db9ec823/backtrace-0.3.46/src/backtrace/mod.rs:66
   2: std::sys_common::backtrace::_print_fmt
             at src/libstd/sys_common/backtrace.rs:78
   3: <std::sys_common::backtrace::_print::DisplayBacktrace as core::fmt::Display>::fmt
             at src/libstd/sys_common/backtrace.rs:59
   4: core::fmt::write
             at src/libcore/fmt/mod.rs:1076
   5: std::io::Write::write_fmt
             at src/libstd/io/mod.rs:1537
   6: std::sys_common::backtrace::_print
             at src/libstd/sys_common/backtrace.rs:62
   7: std::sys_common::backtrace::print
             at src/libstd/sys_common/backtrace.rs:49
   8: std::panicking::default_hook::{{closure}}
             at src/libstd/panicking.rs:198
   9: std::panicking::default_hook
             at src/libstd/panicking.rs:218
  10: std::panicking::rust_panic_with_hook
             at src/libstd/panicking.rs:486
  11: rust_begin_unwind
             at src/libstd/panicking.rs:388
  12: core::panicking::panic_fmt
             at src/libcore/panicking.rs:101
  13: core::panicking::panic
             at src/libcore/panicking.rs:56
  14: core::option::Option<T>::unwrap
             at /home/void/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/macros/mod.rs:10
  15: bevy_wgpu::wgpu_renderer::WgpuRenderer::new::{{closure}}
             at crates/bevy_wgpu/src/wgpu_renderer.rs:22
  16: <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll
             at /home/void/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libcore/future/mod.rs:73
  17: pollster::block_on
             at /home/void/.cargo/registry/src/githubproxy.fjygbaifeng.eu.org-1ecc6299db9ec823/pollster-0.2.0/src/lib.rs:64
  18: bevy_wgpu::wgpu_render_system
             at crates/bevy_wgpu/src/lib.rs:35
  19: <bevy_wgpu::WgpuPlugin as bevy_app::plugin::Plugin>::build
             at crates/bevy_wgpu/src/lib.rs:22
  20: bevy_app::app_builder::AppBuilder::add_plugin
             at ./crates/bevy_app/src/app_builder.rs:235
  21: <bevy_app::app_builder::AppBuilder as bevy::add_default_plugins::AddDefaultPlugins>::add_default_plugins
             at src/add_default_plugins.rs:33
  22: breakout::main
             at examples/game/breakout.rs:9
  23: std::rt::lang_start::{{closure}}
             at /home/void/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:67
  24: std::rt::lang_start_internal::{{closure}}
             at src/libstd/rt.rs:52
  25: std::panicking::try::do_call
             at src/libstd/panicking.rs:297
  26: std::panicking::try
             at src/libstd/panicking.rs:274
  27: std::panic::catch_unwind
             at src/libstd/panic.rs:394
  28: std::rt::lang_start_internal
             at src/libstd/rt.rs:51
  29: std::rt::lang_start
             at /home/void/.rustup/toolchains/stable-x86_64-unknown-linux-gnu/lib/rustlib/src/rust/src/libstd/rt.rs:67
  30: main
  31: __libc_start_main
             at ../csu/libc-start.c:308
  32: _start
             at ../sysdeps/x86_64/start.S:120
note: Some details are omitted, run with `RUST_BACKTRACE=full` for a verbose backtrace.