Use new STARR for scalaVersion override in scala-{xml,parsers}

This was necessary to get a community build working with the
scala/scala#5003.

It is likely that after this change, people will need to rebase
branches on scala/scala#2.12.x before running them through the
community build. Alternatively, they could trigger the community
build with community-builds/64063200, rather than 64063200#2.12.x.

Author: retronym

community.dbuild

@@ -43,12 +43,12 @@ build += {
       {
         name: "scala-xml"
         uri: "https://github.com/"${vars.scala-xml-ref}
-        extra.commands: "set scalaVersion := \"2.12.0-M3\""
+        extra.commands: "set scalaVersion := \"2.12.0-M3-dc9effe\""
       }
       {
         name: "scala-parser-combinators"
         uri: "https://github.com/"${vars.scala-parser-combinators-ref}
-        extra.commands: "set scalaVersion := \"2.12.0-M3\""
+        extra.commands: "set scalaVersion := \"2.12.0-M3-dc9effe\""
         extra.projects: ["scala-parser-combinatorsJVM"]
       }
     ]