Bracket Push - Update to Scala 2.12.1 - refs exercism#235. Add topics to config.json - refs exercism#125.

Author: ricemery

config.json

@@ -296,6 +296,8 @@
       "slug": "bracket-push",
       "difficulty": 1,
       "topics": [
+         "Strings",
+         "Parsing"
       ]
 		},
     {

exercises/bracket-push/build.sbt

@@ -1,4 +1,4 @@
-scalaVersion := "2.11.8"
+scalaVersion := "2.12.1"
 
-libraryDependencies += "org.scalatest" % "scalatest_2.11" % "2.2.5" % "test"
-libraryDependencies += "org.scala-lang.modules" %% "scala-parser-combinators" % "1.0.4"
+libraryDependencies += "org.scalatest" %% "scalatest" % "3.0.1" % "test"
+libraryDependencies += "org.scala-lang.modules" %% "scala-parser-combinators" % "1.0.5"