Specify the runs option for external code coverage.

.scrutinizer.yml

@@ -2,4 +2,5 @@ imports:
     - php
 
 tools:
-    external_code_coverage: true
+    external_code_coverage:
+        runs: 5 # No Code Coverage on PHP 5.2 and HHVM

.travis.yml

@@ -1,5 +1,7 @@
 language: php
 
+# When adding environments here, the number of runs specified in .scrutinizer.yml
+# may have to be adjusted.
 php:
   - 5.2
   - 5.3.3