Revert "MNT: add _version.py to .gitignore"

Author: rcomer

.gitignore

@@ -44,8 +44,6 @@ pip-wheel-metadata/*
 # build subproject files
 subprojects/*/
 !subprojects/packagefiles/
-# file generated by setuptools_scm
-_version.py
 
 # OS generated files #
 ######################