GQL-111: Updates UMM-C version to 1.18.4 (#163)

Author: dmistry1

cdk/graphql/lib/graphql-stack.ts

@@ -38,7 +38,7 @@ const environment = {
   stellateAppName: process.env.STELLATE_APP_NAME!,
   stellateKey: process.env.STELLATE_KEY!,
   lambdaTimeout: process.env.LAMBDA_TIMEOUT || '30',
-  ummCollectionVersion: '1.18.3',
+  ummCollectionVersion: '1.18.4',
   ummGranuleVersion: '1.6.5',
   ummOrderOptionVersion: '1.0.0',
   ummServiceVersion: '1.5.3',