Numbers are acceptable in the method name

fixes gh-518

spring-cloud-contract-verifier/src/main/groovy/org/springframework/cloud/contract/verifier/util/NamesUtil.groovy

@@ -116,8 +116,7 @@ class NamesUtil {
 	 * Converts illegal characters in method names to underscores
 	 */
 	static String convertIllegalMethodNameChars(String methodName) {
-		String result =  methodName.replaceAll('^[^a-zA-Z_$]', '_')
-		result = result.replaceAll('[^a-zA-Z_$0-9]', '_')
-		return result
+		String result =  methodName.replaceAll('^[^a-zA-Z_$0-9]', '_')
+		return result.replaceAll('[^a-zA-Z_$0-9]', '_')
 	}
 }

spring-cloud-contract-verifier/src/test/groovy/org/springframework/cloud/contract/verifier/builder/MethodBuilderSpec.groovy

@@ -25,10 +25,11 @@ class MethodBuilderSpec extends Specification {
             }
             ContractMetadata metadata = new ContractMetadata(null, false, 0, null, contractDsl)
         when:
-            File stubFile = new File("5invalid-method:name.groovy")
+            File stubFile = new File("invalid-method:name.groovy")
+
             String methodName = MethodBuilder.methodName(metadata, stubFile, contractDsl)
         then:
-            methodName.equals("_invalid_method_name")
+            methodName == "invalid_method_name"
     }
 
 }

spring-cloud-contract-verifier/src/test/groovy/org/springframework/cloud/contract/verifier/util/NamesUtilSpec.groovy

@@ -109,6 +109,6 @@ class NamesUtilSpec extends Specification {
 		given:
 			String string = '10a-b c.1.0.x+d1174$dd'
 		expect:
-			NamesUtil.convertIllegalMethodNameChars(string) == '_0a_b_c_1_0_x_d1174$dd'
+			NamesUtil.convertIllegalMethodNameChars(string) == '10a_b_c_1_0_x_d1174$dd'
 	}
 }