Drop support for go 1.2 (#10)

* Drop support for go 1.2

Also, add all the go versions in between 1.6 and tip to the Travis test script.

Author: erik

.travis.yml

@@ -1,8 +1,14 @@
 language: go
 go:
-  - 1.2
   - 1.3
   - 1.4
   - 1.5
+  - 1.6
+  - 1.7
+  - 1.8
+  - 1.9
+  - "1.10"
+  - 1.11
+  - 1.12
   - tip
 script: go test -v ./...