Fix build

Author: mohamedsamehsalah

refaster-support/src/main/java/tech/picnic/errorprone/refaster/matchers/IsFunctionReturningMono.java

@@ -9,6 +9,7 @@
 import com.sun.source.tree.LambdaExpressionTree;
 import com.sun.source.tree.Tree;
 import com.sun.source.tree.Tree.Kind;
+import java.util.function.Function;
 
 /**
  * A matcher of lambda expressions that are of type {@code java.util.function.Function} that returns
@@ -19,7 +20,7 @@ public final class IsFunctionReturningMono implements Matcher<ExpressionTree> {
   private static final Matcher<Tree> MONO_TYPE =
       isSameType(Suppliers.typeFromString("reactor.core.publisher.Mono"));
   private static final Matcher<Tree> FUNCTION_TYPE =
-      isSameType(Suppliers.typeFromString("java.util.function.Function"));
+      isSameType(Suppliers.typeFromString(Function.class.getCanonicalName()));
 
   /** Instantiates a new {@link IsFunctionReturningMono} instance. */
   public IsFunctionReturningMono() {}

refaster-support/src/test/java/tech/picnic/errorprone/refaster/matchers/IsFunctionReturningMonoTest.java

@@ -19,12 +19,12 @@ void matches() {
             "import reactor.core.publisher.Mono;",
             "",
             "class A {",
-            "// BUG: Diagnostic contains:",
-            " Function<String, Mono<String>> positive = s -> Mono.just(s);",
+            "  // BUG: Diagnostic contains:",
+            "  Function<String, Mono<String>> positive = s -> Mono.just(s);",
             "",
-            " Function<String, Flux<String>> negative = s -> Flux.just(s);",
+            "  Function<String, Flux<String>> negative = s -> Flux.just(s);",
             "",
-            " Supplier<Mono<String>> negative2 = () -> Mono.just(\"s\");",
+            "  Supplier<Mono<String>> negative2 = () -> Mono.just(\"s\");",
             "}")
         .doTest();
   }