Refactor travis config to include osx, dmd-beta, ldc2 and dub.

.travis.sh

@@ -0,0 +1,12 @@
+#!/bin/bash
+
+set -e
+
+dub build --build=release
+git submodule update --init --recursive
+
+if [ $DC = ldc2 ]; then
+    make test DC=ldmd2
+else
+    make test
+fi

.travis.yml

@@ -1,5 +1,11 @@
 sudo: false
 language: d
-script:
-    - git submodule update --init --recursive
-    - make test
+d:
+  - dmd-beta
+  - dmd
+  - ldc
+os:
+  - linux
+  - osx
+
+script: ./.travis.sh