Move PHP default threshold to 28

When analyzing the WordPress project at the current default mass
threshold of 10, it was observed that Duplications found only by
Platform had masses of 27 or less, while Duplications found by both
Platform and Classic had masses of 28 or greater. Note: there were no
Duplications found only by Classic.

Therefore, a threshold of 28 should ensure an analysis on Platform emits
the same Duplication issues as on Classic.

Author: pbrisbin

lib/cc/engine/analyzers/php/main.rb

@@ -14,7 +14,7 @@ class Main < CC::Engine::Analyzers::Base
             "**/*.inc",
             "**/*.module"
           ]
-          DEFAULT_MASS_THRESHOLD = 10
+          DEFAULT_MASS_THRESHOLD = 28
           POINTS_PER_OVERAGE = 100_000
 
           private