*: remove Go 1.7 support

.travis.yml

@@ -1,6 +1,5 @@
 language: go
 go:
-  - 1.7.x
   - 1.8.x
   - 1.9.x
   - 1.10.x

gogs.go

@@ -1,4 +1,4 @@
-// +build go1.7
+// +build go1.8
 
 // Copyright 2014 The Gogs Authors. All rights reserved.
 // Use of this source code is governed by a MIT-style