Bug: 'Eterm' → 'eterm' in getColorDepth

[sttk]

I found a bug of getColorDepth at this line.
Elements of TERM_ENVS should be lower case because they are compared with lower case of env.TERM.

[ofrobots]

@sttk do you want to try opening a pull-request for this? You can find a contribution guide here.

[Dlewis89]

I would like to take a shot at this if sttk doesnt want too.

[sttk]

@Dlewis89 OK. I ask you this pr.