Add Go 1.8 test, and drop 1.2~1.4

Author: methane

.travis.yml

@@ -1,12 +1,10 @@
 sudo: false
 language: go
 go:
-  - 1.2
-  - 1.3
-  - 1.4
   - 1.5
   - 1.6
   - 1.7
+  - 1.8
   - tip
 
 before_script:

README.md

@@ -37,7 +37,7 @@ A MySQL-Driver for Go's [database/sql](https://golang.org/pkg/database/sql/) pac
   * Optional placeholder interpolation
 
 ## Requirements
-  * Go 1.2 or higher
+  * Go 1.5 or higher
   * MySQL (4.1+), MariaDB, Percona Server, Google CloudSQL or Sphinx (2.2.3+)
 
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