Default LC_ALL to parent process value

The InvalidByteSequenceError we're seeing running under rake stems from mixlib shell (which this gem uses) defaulting LC_ALL to 'C'.
https://github.com/opscode/mixlib-shellout/blob/master/lib/mixlib/shellout.rb#L30
https://github.com/opscode/mixlib-shellout/blob/master/lib/mixlib/shellout.rb#L305

This PR ensure we're always passing an LC_ALL environment key to mixlib shell to keep it form forcing a default LC_ALL value of 'C'.