Fixed rtd_theme finding
Fixed rtd_theme finding

According to https://github.com/choderalab/pymbar/commit/56ff6b04049a6dd4130b78742c45c6bd0c8de84d this is the 'correct' way to include and use the rtd theme. Works for me on three different machines (Fedora 22, Suse 42.1, Debian Sid) with system side installed rtd theme.
aleibl/openxpki,aleibl/openxpki,aleibl/openxpki,stefanomarty/openxpki,openxpki/openxpki,stefanomarty/openxpki,oliwel/openxpki,aleibl/openxpki,stefanomarty/openxpki,oliwel/openxpki,aleibl/openxpki,stefanomarty/openxpki,stefanomarty/openxpki,oliwel/openxpki,openxpki/openxpki,oliwel/openxpki,openxpki/openxpki,aleibl/openxpki,stefanomarty/openxpki,oliwel/openxpki,openxpki/openxpki,oliwel/openxpki