(#307) Fix plan parsing in JSON spec tests

Previously, parsing of Puppet plan code failed in json_spec.rb because
it didn’t provide a file name to the parser, which prevented the parser
from enabling task support in Puppet, which prevented the parser from
recognizing a plan.

This turns on task support in Puppet before trying to parse a plan in
json_spec.rb.

Author: danielparks

spec/unit/puppet-strings/json_spec.rb

@@ -25,6 +25,8 @@ class klass(Integer $param1, $param2, String $param3 = hi) inherits foo::bar {
 }
     SOURCE
 
+    # Puppet will not parse plans if Puppet[:tasks] is not enabled.
+    Puppet[:tasks] = true if TEST_PUPPET_PLANS
     expect(YARD::Parser::SourceParser.parse_string(<<-SOURCE, :puppet).enumerator.length).to eq(1) if TEST_PUPPET_PLANS
 # A simple plan.
 # @param param1 First param.