clear composer cache before install, as per vimeo/psalm

SignpostMarv · SignpostMarv · commit 8250289a2e23 · 2020-01-11T21:09:19.000Z
diff --git a/.travis.yml b/.travis.yml
@@ -6,6 +6,7 @@ php:
     - 7.4 # Psalm does not support 7.4 yet (uses Fn)
 before_install:
     - phpenv config-rm xdebug.ini || true
+    - composer clear-cache
 
 install:
   - composer install
