Bump gitdb2 upper constraint to 4.0.2

Per [1], 4.0.1 has been deleted because it was lacking proper signature
keys.

[1] gitpython-developers/gitdb#59

Change-Id: Id8ebe2962f3a099f343db1428dc846380f556fd9
Signed-off-by: Stephen Finucane <[email protected]>

Author: stephenfin

upper-constraints.txt

@@ -773,8 +773,8 @@ oslo.utils===4.0.0;python_version=='3.6'
 oslo.utils===4.0.0;python_version=='3.7'
 python-editor===1.0.4
 gitdb2===2.0.6;python_version=='2.7'
-gitdb2===4.0.1;python_version=='3.6'
-gitdb2===4.0.1;python_version=='3.7'
+gitdb2===4.0.2;python_version=='3.6'
+gitdb2===4.0.2;python_version=='3.7'
 requests-kerberos===0.12.0
 itsdangerous===1.1.0
 XStatic-jquery-ui===1.12.1.1