audit: audit version_scheme.

Reuse the existing `revision` method that was made more generic.

Library/Homebrew/cmd/audit.rb

@@ -623,12 +623,12 @@ class FormulaAuditor
     end
   end
 
-  def audit_revision
+  def audit_revision_and_version_scheme
     return unless formula.tap # skip formula not from core or any taps
     return unless formula.tap.git? # git log is required
 
     fv = FormulaVersions.new(formula, :max_depth => 10)
-    attributes = [:revision]
+    attributes = [:revision, :version_scheme]
     attributes_map = fv.version_attributes_map(attributes, "origin/master")
 
     attributes.each do |attribute|
@@ -1016,7 +1016,7 @@ class FormulaAuditor
     audit_formula_name
     audit_class
     audit_specs
-    audit_revision
+    audit_revision_and_version_scheme
     audit_desc
     audit_homepage
     audit_bottle_spec