Use a singleton PropertyFetcher by default - tweaked tests

Author: bbakerman

src/test/groovy/graphql/execution/instrumentation/InstrumentationTest.groovy

@@ -15,6 +15,7 @@ import graphql.schema.DataFetcher
 import graphql.schema.DataFetchingEnvironment
 import graphql.schema.LightDataFetcher
 import graphql.schema.PropertyDataFetcher
+import graphql.schema.SingletonPropertyDataFetcher
 import graphql.schema.StaticDataFetcher
 import org.awaitility.Awaitility
 import org.jetbrains.annotations.NotNull
@@ -100,7 +101,7 @@ class InstrumentationTest extends Specification {
 
         instrumentation.dfClasses.size() == 2
         instrumentation.dfClasses[0] == StaticDataFetcher.class
-        LightDataFetcher.class.isAssignableFrom(instrumentation.dfClasses[1])
+        instrumentation.dfClasses[1] == SingletonPropertyDataFetcher.class
 
         instrumentation.dfInvocations.size() == 2