Adds tests for PHP 7.3

Author: mariusbalcytis

.travis.yml

@@ -8,18 +8,22 @@ env:
 
 matrix:
     include:
-      - php: 7.0
+      - php: "7.0"
         env: COMPOSER_ARGS=""
-      - php: 7.1
+      - php: "7.1"
         env: COMPOSER_ARGS=""
-      - php: 7.2
+      - php: "7.2"
         env: COMPOSER_ARGS="" WITH_CS="true"
+      - php: "7.3"
+        env: COMPOSER_ARGS=""
 
-      - php: 7.0
+      - php: "7.0"
+        env: COMPOSER_ARGS="--prefer-lowest"
+      - php: "7.1"
         env: COMPOSER_ARGS="--prefer-lowest"
-      - php: 7.1
+      - php: "7.2"
         env: COMPOSER_ARGS="--prefer-lowest"
-      - php: 7.2
+      - php: "7.3"
         env: COMPOSER_ARGS="--prefer-lowest"
 
 cache: