travis: remove support for 1.2

.travis.yml

diff --git a/.travis.yml b/.travis.yml
index 2d8c086..ec64114 100644
--- a/.travis.yml
+++ b/.travis.yml
@@ -1,6 +1,5 @@
 language: go
 go:
-  - 1.2
   - 1.3
   - 1.4
   - tip