Fix reference for python icon.
Fix reference for python icon.

While using awesome-terminal-fonts it is recommended to use `\ue63c` to
reference python icon instead of `\U1F40D` (that wasn't even working).
Ref:
https://github.com/gabrielelana/awesome-terminal-fonts/issues/38#issuecomment-302939451

bhilburn/powerlevel9k,natemccurdy/powerlevel9k,dritter/powerlevel9k,rjorgenson/powerlevel9k,natemccurdy/powerlevel9k,dritter/powerlevel9k,rjorgenson/powerlevel9k,bhilburn/powerlevel9k