Remove the optional ':' and EOL delimiter from code complete loc regex

Hello!

On Cygwin there appears to be some issue with the code completion location regex or its implementation - for every request I get the error message:

Can't decode argument for --code-complete-at [/home/Brian/elisp/foreign/rtags/src/RClient.cpp:1087:9:]

Though I'm not sure what the underlying issue is, when I tried removing the optional `:` capture it works as intended.  I verified this change working on both my linux and cygwin machines.