add twitter-util to 2.12 projects list

Author: SethTisue

projects-2.12.md

@@ -73,6 +73,7 @@ Add in sbt using `libraryDependencies += ...`:
     "com.thoughtworks.each"            %% "each"                      % "3.1.1"
     "com.thoughtworks.enableIf"        %% "enableif"                  % "1.1.4"
     "com.thoughtworks.extractor"       %% "extractor"                 % "1.1.1"
+    "com.twitter"                      %% "util-core"                 % "6.39.0"
     "com.typesafe.akka"                %% "akka-actor"                % "2.4.12"
     "com.typesafe.akka"                %% "akka-stream"               % "2.4.12"
     "com.typesafe.akka"                %% "akka-http-core"            % "10.0.0"