gitlab: Switch to Go 1.6

gitlab-workhorse works perfectly fine with it, so switch to current stable golang.

software/gitlab/software.cfg

@@ -23,7 +23,7 @@ extends =
 
 parts =
     ruby2.1
-    golang15
+    golang16
     git
     postgresql92
     redis28
@@ -175,7 +175,7 @@ configure-command = :
 make-targets= ${:_buildout_section_name_}
 
 environment =
-  PATH=${golang15:location}/bin:%(PATH)s
+  PATH=${golang16:location}/bin:%(PATH)s
 
 
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