travis: Install the latest happy first

eagletmt · eagletmt · commit 186cf66f65db · 2015-07-26T17:27:50.000+09:00
diff --git a/install-deps.sh b/install-deps.sh
@@ -17,4 +17,5 @@ fi
 make -f make_unix.mak
 
 cabal update
-cabal install ghc-mod
+cabal install happy
+cabal install -j ghc-mod
