use to_h instead of to_hash

apparently ruby 2 adds this as a standard method so
we should stay compliant

lib/metasploit/framework/credential.rb

@@ -90,7 +90,11 @@ module Metasploit
         self
       end
 
-      def to_hash
+      # This method takes all of the attributes of the {Credential} and spits
+      # them out in a hash compatible with the create_credential calls.
+      #
+      # @return [Hash] a hash compatible with #create_credential
+      def to_h
         {
             private_data: private,
             private_type: private_type,

spec/lib/metasploit/framework/credential_spec.rb

@@ -143,7 +143,7 @@ describe Metasploit::Framework::Credential do
     end
   end
 
-  describe '#to_hash' do
+  describe '#to_h' do
     subject(:cred_detail) do
       described_class.new(public: public, private: private, realm: realm, realm_key: realm_type, private_type: private_type)
     end
@@ -155,7 +155,7 @@ describe Metasploit::Framework::Credential do
           realm_key: realm_type,
           realm_value: realm
       }
-      expect(cred_detail.to_hash).to eq cred_hash
+      expect(cred_detail.to_h).to eq cred_hash
     end
   end
 end