HADOOP-13640. Fix findbugs warning in VersionInfoMojo.java. Contributed by Yuanbo Liu.

(cherry picked from commit 82c55dcbc8e3d5314aae9f8f600c660759213e45)
(cherry picked from commit 25df276c6b24db46070c9885e48e363cc92d1b6f)

Conflicts:
    hadoop-maven-plugins/src/main/java/org/apache/hadoop/maven/plugin/versioninfo/VersionInfoMojo.java

hadoop-maven-plugins/src/main/java/org/apache/hadoop/maven/plugin/versioninfo/VersionInfoMojo.java

@@ -160,7 +160,7 @@ public class VersionInfoMojo extends AbstractMojo {
         if (index > -1) {
           res[0] = path.substring(0, index - 1);
           int branchIndex = index + "branches".length() + 1;
-          index = path.indexOf("/", branchIndex);
+          index = path.indexOf('/', branchIndex);
           if (index > -1) {
             res[1] = path.substring(branchIndex, index);
           } else {