Remove redundant static modifier for enums

Closes gh-526

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/JsonFieldPath.java

@@ -127,7 +127,7 @@ final class JsonFieldPath {
 	/**
 	 * The type of a field path.
 	 */
-	static enum PathType {
+	enum PathType {
 
 		/**
 		 * The path identifies a single item in the payload.

spring-restdocs-core/src/main/java/org/springframework/restdocs/payload/JsonFieldProcessor.java

@@ -195,7 +195,7 @@ final class JsonFieldProcessor {
 					|| this.matchType == MatchType.NULL;
 		}
 
-		private static enum MatchType {
+		private enum MatchType {
 
 			ABSENT, MIXED, NONE, NULL, NON_NULL;