Temporary removed sigmac run from Travis configuration

* sigmac actually doesn't supports all features used in Sigma rules.
* It returns the wrong exit code on parse errors. Parse failures cause
  passed builds.

.travis.yml

@@ -8,4 +8,4 @@ install:
 
 script:
   - yamllint .
-  - for f in rules/windows/builtin/*; do python tools/sigmac.py -v $f; done
+#  - for f in rules/windows/builtin/*; do python tools/sigmac.py -v $f; done