Convert csh_ldap git uri to pypi in requirements.txt

Converts the csh_ldap requirement from a git uri to the pypi package, along with semantic versioning requiring csh_ldap version >= 2.3.1

The requirement for csh_ldap version being >= 2.3.1 is based on soon-to-be-implemented healthchecking, which will be dependent on the changes made in this version.

Author: adamhb123

requirements.txt

@@ -2,7 +2,7 @@ alembic~=0.9.8
 astroid~=2.2.5
 blinker~=1.4
 click~=6.7
-git+git://github.com/mxmeinhold/csh_ldap@c441add834405761758bea981fd5286f2abcaf93#egg=csh_ldap
+csh_ldap>=2.3.1
 Flask~=1.1.0
 Flask-Migrate~=2.1.1
 Flask-Gzip~=0.2