Remove redundant static modifier for enums

Closes gh-526

Author: izeye

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

@@ -127,7 +127,7 @@ private static List<String> extractDotSeparatedSegments(String path) {
 /**
  * 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 @@ boolean fieldFound() {
 || this.matchType == MatchType.NULL;
 }
 
-private static enum MatchType {
+private enum MatchType {
 
 ABSENT, MIXED, NONE, NULL, NON_NULL;