Upgrade gin-gonic to latest master, fix compatibility issues

vendor/github.com/gin-gonic/gin/.travis.yml

@@ -1,6 +1,31 @@
 language: go
 sudo: false
 go:
-  - 1.3
-  - 1.4
-  - tip
+  - 1.6.x
+  - 1.7.x
+  - 1.8.x
+  - master
+
+git:
+  depth: 3
+
+install:
+  - make install
+
+script:
+  - make vet
+  - make fmt-check
+  - make embedmd
+  - make misspell-check
+  - make test
+
+after_success:
+  - bash <(curl -s https://codecov.io/bash)
+
+notifications:
+  webhooks:
+    urls:
+      - https://webhooks.gitter.im/e/7f95bf605c4d356372f4
+    on_success: change  # options: [always|never|change] default: always
+    on_failure: always  # options: [always|never|change] default: always
+    on_start: false     # default: false