Allow dashes in variable key names

It can be confusing when adding variables to templates and macros to
discover that '-' are not valid characters in the key name.

Change-Id: I8b10371ddac54c19a92a9d0811cd549a492b3dbb

jenkins_jobs/formatter.py

@@ -84,7 +84,7 @@ class CustomFormatter(Formatter):
     _expr = """
         (?<!{){({{)*                # non-pair opening {
         (?:obj:)?                   # obj:
-        (?P<key>\w+)                # key
+        (?P<key>[\w\-]+)            # key
         (?:\|(?P<default>[^}]*))?   # default fallback
         }(}})*(?!})                 # non-pair closing }
     """