simple-munin-plugin beta regression

[est31]

simple-munin-plugin version 0.1.0 test-regressed from stable to beta (full log):

Aug 16 21:31:15.784 INFO blam! ---- tests::test_get_env_threshold_as_number stdout ----
Aug 16 21:31:15.784 INFO blam! 	thread 'tests::test_get_env_threshold_as_number' panicked at 'assertion failed: `(left == right)`
Aug 16 21:31:15.785 INFO blam!   left: `Some(2.5)`,
Aug 16 21:31:15.785 INFO blam!  right: `Some(10)`', src/lib.rs:134:8
Aug 16 21:31:15.785 INFO blam! note: Run with `RUST_BACKTRACE=1` for a backtrace.

cc @yshryk

[alexcrichton]

Test uses environment variables, buggy test.