deps: pin pyparsing<3.1.0

The 3.1.0 release of pyparsing introduced a change
or regression in the error message that we parse
in the gabbit tests so we pin until that is investigated
in the issue [1].

[1] pyparsing/pyparsing#504

setup.cfg

@@ -47,7 +47,9 @@ install_requires =
     Paste
     PasteDeploy
     daiquiri
-    pyparsing>=2.2.0
+    # TODO(tobias-urdin): Evaluate unpin later
+    # https://github.com/pyparsing/pyparsing/issues/504
+    pyparsing>=2.2.0,<3.1.0
     lz4>=0.9.0
     tooz>=1.38
     cachetools