add more recent releases, quote the versions

Per Travis.ci doc: https://docs.travis-ci.com/user/languages/go/#specifying-a-go-version-to-use

.travis.yml

@@ -1,13 +1,16 @@
 language: go
 
 go:
-    - 1.3
-    - 1.4
-    - 1.5
-    - 1.6
-    - 1.7
-    - 1.8
-    - 1.9
+    - "1.3"
+    - "1.4"
+    - "1.5"
+    - "1.6"
+    - "1.7"
+    - "1.8"
+    - "1.9"
+    - "1.10"
+    - "1.11"
+    - "1.12"
 
 script:
     - ./validate.sh