fixed bug in cleanup_moltemplate.sh

Fixed bug #86 which prevented cleanup_moltemplate.sh from working whenever "moltemplate" was installed using pip or pip3.

(This bug did not effect the small number of users like me who install moltemplate by other means.)

All credit belongs to github user PhnRvTjN (Phani Ravi Teja Nunna) for solving the bug, and to github user yurivict for reporting the bug!