Extraneous output (`{}`) when running `BuildTask`

[chancancode]

I believe this line is intended for printing the command we are about to execute. However, when called in this form it causes the console output to look like this:

{}
cargo rustc --release -- -C link-args=-Wl,-undefined,dynamic_lookup

...or sometimes...

{"HELIX_LIB_DIR"=>"/Users/godfrey/Code/helix/ruby/windows_build"}
cargo rustc --release -- -C link-args=-Wl,-undefined,dynamic_lookup

[wagenet]

The system command can take a hash of ENV variables. However, when we're empty it prints an empty hash. We could probably make the run method signature run(env, cmd) and then only print env if it isn't empty.