Merge pull request #900 from PENEKhun

* gh-900:
  Avoid substring creation when string part to StringBuilder

Closes gh-900

spring-restdocs-core/src/main/java/org/springframework/restdocs/operation/preprocess/UriModifyingOperationPreprocessor.java

@@ -213,7 +213,7 @@ private String modify(String input) {
 			while (matcher.find()) {
 				for (int i = 1; i <= matcher.groupCount(); i++) {
 					if (matcher.start(i) >= 0) {
-						builder.append(input.substring(previous, matcher.start(i)));
+						builder.append(input, previous, matcher.start(i));
 					}
 					if (matcher.start(i) >= 0) {
 						previous = matcher.end(i);