Fixed the way regex entries are generated for message bodies

fixes gh-858

spring-cloud-contract-spec/src/main/groovy/org/springframework/cloud/contract/spec/internal/CanBeDynamic.java

@@ -0,0 +1,31 @@
+/*
+ * Copyright 2013-2018 the original author or authors.
+ *
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ *
+ */
+
+package org.springframework.cloud.contract.spec.internal;
+
+/**
+ * Some properties can contain dynamic values.
+ * If that's the case we need to know how to generate a concrete value for them.
+ *
+ * @since 2.1.0
+ */
+public interface CanBeDynamic {
+	/**
+	 * @return a generated, concrete value
+	 */
+	Object generateConcreteValue();
+}