Fix stringbuilder to stringBuffer to make the java (non google versio…

…n) happy.

Otherwise this code does not compile outside google.
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Created by MOE: https://github.com/google/moe
MOE_MIGRATED_REVID=122885192

src/main/java/com/google/api/tools/framework/aspects/documentation/model/DocumentationUtil.java

@@ -193,7 +193,7 @@ public static String removeCrossReference(String text) {
     Pattern pattern = Pattern.compile("\\[(?<name>[^\\]]+?)\\]( |\\n)*"
         + "\\[(?<link>[^\\]]*?)\\]");
     Matcher matcher = pattern.matcher(text);
-    StringBuilder result = new StringBuilder();
+    StringBuffer result = new StringBuffer();
     while (matcher.find()) {
       String replacementText = matcher.group("name");
       replacementText = Matcher.quoteReplacement(replacementText);