(#270) lock file was generated on 7.2, needs removing so 7.0 unit tes…

…ts "pass"

.travis.yml

@@ -4,9 +4,9 @@ sudo: false
 
 matrix:
   include:
-    - php: 5.6
     - php: 7.0
     - php: 7.1
+    - php: 7.2
       env: WITH_COVERAGE=true
     - php: nightly
   allow_failures:
@@ -24,6 +24,7 @@ before_install:
   - travis_retry composer self-update
 
 install:
+  - rm composer.lock
   - travis_retry composer install --no-interaction --prefer-dist --no-suggest;
 
 script: