Remove mysql8 from CI

wercker.yml

@@ -9,13 +9,6 @@ services:
           MYSQL_USER: gorm
           MYSQL_PASSWORD: gorm
           MYSQL_RANDOM_ROOT_PASSWORD: "yes"
-    - name: mysql
-      id: mysql:8
-      env:
-          MYSQL_DATABASE: gorm
-          MYSQL_USER: gorm
-          MYSQL_PASSWORD: gorm
-          MYSQL_RANDOM_ROOT_PASSWORD: "yes"
     - name: mysql57
       id: mysql:5.7
       env:
@@ -109,11 +102,6 @@ build:
                 code: |
                     GORM_DIALECT=mysql GORM_DSN="gorm:gorm@tcp(mariadb:3306)/gorm?charset=utf8&parseTime=True" go test ./...
 
-        - script:
-                name: test mysql
-                code: |
-                    GORM_DIALECT=mysql GORM_DSN="gorm:gorm@tcp(mysql:3306)/gorm?charset=utf8&parseTime=True" go test ./...
-
         - script:
                 name: test mysql5.7
                 code: |