Pin missing eggs

Since f427842b some software releases has been
found to be without pinnsed eggs for GitPython dependency.

/reviewed-on nexedi/slapos!432

stack/slapos.cfg

@@ -156,6 +156,14 @@ Flask = 0.12
 # slapos.toolbox==0.81
 GitPython = 2.1.11
 
+# Required by:
+# GitPython==2.1.11
+gitdb2 = 2.0.5
+
+# Required by:
+# gitdb==2.0.5
+smmap2 = 2.0.5
+
 # Required by:
 # slapos.toolbox==0.81
 PyRSS2Gen = 1.1