Stop using deprecated StringEscapeUtils from commons-lang3

Since version 3.6 of lang3, StringEscapeUtils is deprecated in favor
of the class of the same name in commons-text.

Add a dependency on commons-text, and use StringEscapeUtils from there
instead.

Keep the dependency on commons-lang3 since there is still a dependency
on it (TocFormatter uses StringUtils).

Change-Id: I99448c811672c9ac293e88acbeb99d566a8aebe7

java/com/google/gitiles/HtmlDiffFormatter.java

diff --git a/java/com/google/gitiles/HtmlDiffFormatter.java b/java/com/google/gitiles/HtmlDiffFormatter.java
index 666d5a2..44d2c18 100644
--- a/java/com/google/gitiles/HtmlDiffFormatter.java
+++ b/java/com/google/gitiles/HtmlDiffFormatter.java
@@ -24,7 +24,7 @@
 import java.io.OutputStream;
 import java.util.List;
 import java.util.Map;
-import org.apache.commons.lang3.StringEscapeUtils;
+import org.apache.commons.text.StringEscapeUtils;
 import org.eclipse.jgit.diff.DiffEntry;
 import org.eclipse.jgit.diff.DiffEntry.ChangeType;
 import org.eclipse.jgit.diff.DiffFormatter;