Remove leading https:// from gitter link text

Author: dstansby

cheatsheets.tex

@@ -328,7 +328,7 @@
     \href{https://stackoverflow.com/questions/tagged/matplotlib}
          {\faIcon{stack-overflow}\,stackoverflow.com/questions/tagged/matplotlib}\\
     \href{https://app.gitter.im/#/room/#matplotlib_matplotlib:gitter.im}
-         {\faIcon{gitter}\,{https://gitter.im/matplotlib/matplotlib}}\\
+         {\faIcon{gitter}\,{gitter.im/matplotlib/matplotlib}}\\
     \href{https://twitter.com/matplotlib}
          {\faIcon{twitter}\,twitter.com/matplotlib}\\
     \href{https://mail.python.org/mailman/listinfo/matplotlib-users}