IndexServlet: Avoid using deprecated SoyFileSet.Builder#add(URL) method
IndexServlet: Avoid using deprecated SoyFileSet.Builder#add(URL) method

The SoyFileSet.Builder#add(URL, String) method should be used instead.
The second parameter is the path to the Soy file which is used for
messages only.

Signed-off-by: Edwin Kempin <d43fb6c98c97e553b671ed9a9318100f1de386e7@google.com>
Change-Id: Id749b9e594c9c4c9ac0ecb27bd20801a0f8964c0

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