SG-16899 httplib2 relative import (#225)

Made the iri2uri import a relative import

Author: eshokrgozar

shotgun_api3/lib/httplib2/README.md

@@ -0,0 +1,5 @@
+Currently this library is pulled from a fork of httplib2 (https://github.com/shotgunsoftware/httplib2)
+
+The reason for the fork is to make a minor fix to the imports that was causing IronPython2.7 ImportErrors. 
+
+The fix has been submitted to httplib2 repo and already merged so this will likely not be necessary as soon as httplib2 is next released. (>v0.17.2) 

shotgun_api3/lib/httplib2/python2/__init__.py

@@ -122,7 +122,7 @@ def _ssl_wrap_socket_unsupported(
     _ssl_wrap_socket = _ssl_wrap_socket_unsupported
 
 if sys.version_info >= (2, 3):
-    from iri2uri import iri2uri
+    from .iri2uri import iri2uri
 else:
 
     def iri2uri(uri):