Disable composer memory limit for failing builds

Author: alcaeus

.travis.yml

@@ -34,10 +34,11 @@ matrix:
     include:
         - php: 5.3
           dist: precise
+          env: COMPOSER_MEMORY_LIMIT=-1
         - php: 5.4
         - php: 5.5
         - php: 5.6
-          env: DEPS="dev"
+          env: DEPS="dev" COMPOSER_MEMORY_LIMIT=-1
         - php: 7.0
         - php: 7.1
         - php: 7.2