update compiler versions on travis build and also build on OSX

.travis.yml

@@ -1,21 +1,24 @@
 language: d
 
 d:
-  - dmd
+  - dmd-2.075.0-b1
+  - dmd-2.074.1
+  - dmd-2.073.2
   - dmd-2.072.2
   - dmd-2.071.2
   - dmd-2.070.2
   - dmd-2.069.2
-  - dmd-2.068.2
-  - dmd-2.074.0-b2
-  - ldc
-  - ldc-1.0.0
-  - ldc-0.17.2
-  - ldc-1.2.0-beta2
+  - ldc-1.3.0-beta2
+  - ldc-1.2.0
+  - ldc-1.1.1
   - gdc
 
 sudo: false
 
+os:
+  - linux
+  - osx
+
 script:
   - dub build --build=release --config=library
   - dub test --build=unittest --config=unittest