Do not crash when referring to a fact key without quoting it

Fixes #118

Author: chutzimir

lib/puppet-lint/plugins/legacy_facts/legacy_facts.rb

@@ -117,7 +117,7 @@ def check
 
       # This matches legacy facts defined in the fact hash that use the top scope
       # fact assignment.
-      if token.value.start_with?('::facts[')
+      if token.value.start_with?("::facts['")
         fact_name = token.value.match(%r{::facts\['(.*)'\]})[1]
 
       # This matches legacy facts defined in the fact hash.

spec/unit/puppet-lint/plugins/legacy_facts/legacy_facts_spec.rb

@@ -121,6 +121,14 @@
         expect(problems).to have(1).problem
       end
     end
+
+    context 'top scoped fact variable using unquoted legacy facts hash variable in interpolation' do
+      let(:code) { '$::facts[osfamily]' }
+
+      it 'detects a single problem' do
+        expect(problems).to have(0).problem
+      end
+    end
   end
 
   context 'with fix enabled' do