build: dry travis yaml

Author: dougwilson

.travis.yml

@@ -10,7 +10,7 @@ node_js:
   - "4.2.0" # Test timers regression
   - "4.9"
   - "5.12"
-  - "6.14"
+  - &lts "6.14"
   - "7.10"
   - "8.12"
   - "9.11"
@@ -23,19 +23,19 @@ env:
     - "DOCKER_MYSQL_TYPE=mysql DOCKER_MYSQL_VERSION=5.7"
 matrix:
   include:
-    - node_js: "6.14"
+    - node_js: *lts
       env: "DOCKER_MYSQL_TYPE=mysql DOCKER_MYSQL_VERSION=5.5"
-    - node_js: "6.14"
+    - node_js: *lts
       env: "DOCKER_MYSQL_TYPE=mysql DOCKER_MYSQL_VERSION=5.6"
-    - node_js: "6.14"
+    - node_js: *lts
       env: "DOCKER_MYSQL_TYPE=mariadb DOCKER_MYSQL_VERSION=5.5"
-    - node_js: "6.14"
+    - node_js: *lts
       env: "DOCKER_MYSQL_TYPE=mariadb DOCKER_MYSQL_VERSION=10.0"
-    - node_js: "6.14"
+    - node_js: *lts
       env: "DOCKER_MYSQL_TYPE=mariadb DOCKER_MYSQL_VERSION=10.1"
-    - node_js: "6.14"
+    - node_js: *lts
       env: "DOCKER_MYSQL_TYPE=mariadb DOCKER_MYSQL_VERSION=10.2"
-    - node_js: "6.14"
+    - node_js: *lts
       env: "DOCKER_MYSQL_TYPE=mariadb DOCKER_MYSQL_VERSION=10.3"
 
 dist: trusty