Test with latest Go patch versions (#693)

.travis.yml

@@ -1,10 +1,10 @@
 sudo: false
 language: go
 go:
-  - 1.7
-  - 1.8
-  - 1.9
-  - tip
+  - 1.7.x
+  - 1.8.x
+  - 1.9.x
+  - master
 
 before_install:
   - go get golang.org/x/tools/cmd/cover
@@ -21,7 +21,7 @@ matrix:
     - env: DB=MYSQL57
       sudo: required
       dist: trusty
-      go: 1.9
+      go: 1.9.x
       services:
         - docker
       before_install:
@@ -43,7 +43,7 @@ matrix:
     - env: DB=MARIA55
       sudo: required
       dist: trusty
-      go: 1.9
+      go: 1.9.x
       services:
         - docker
       before_install:
@@ -65,7 +65,7 @@ matrix:
     - env: DB=MARIA10_1
       sudo: required
       dist: trusty
-      go: 1.9
+      go: 1.9.x
       services:
         - docker
       before_install: