Fix cognito creds

Author: richardwang1124

gems/aws-sdk-cognitoidentity/lib/aws-sdk-cognitoidentity/customizations/cognito_identity_credentials.rb

@@ -94,7 +94,7 @@ def initialize(options = {})
         end
 
         @client = options[:client] || CognitoIdentity::Client.new(
-          client_opts.merge(credentials: false)
+          client_opts.merge(credentials: nil)
         )
         super
       end

gems/aws-sdk-cognitoidentity/spec/cognito_identity_credentials_spec.rb

@@ -38,7 +38,7 @@ module CognitoIdentity
 
         it 'constructs a client with passed arguments when not given' do
           expect(CognitoIdentity::Client).to receive(:new)
-            .with({region: 'us-east-1', credentials: false})
+            .with({region: 'us-east-1', credentials: nil})
             .and_return(client)
 
           creds = CognitoIdentityCredentials.new(
@@ -50,7 +50,7 @@ module CognitoIdentity
 
         it 'excludes before_refresh from client construction' do
           expect(CognitoIdentity::Client).to receive(:new)
-                                               .with({region: 'us-east-1', credentials: false})
+                                               .with({region: 'us-east-1', credentials: nil})
                                                .and_return(client)
 
           creds = CognitoIdentityCredentials.new(