travis: add support for go 1.7 testing

.travis.yml

@@ -1,10 +1,11 @@
 language: go
 sudo: false
 go:
-  - 1.8.x
-  - 1.9.x
-  - tip
+    - 1.7.x  # go testing suite support, which we use, was introduced in go 1.7
+    - 1.8.x
+    - 1.9.x
+    - tip
 script:
-  - go test -tags "alltests" -run Suite -coverprofile coverage.txt github.com/ugorji/go/codec
+    - go test -tags "alltests" -run Suite -coverprofile coverage.txt github.com/ugorji/go/codec
 after_success:
-  - bash <(curl -s https://codecov.io/bash)
+    - bash <(curl -s https://codecov.io/bash)