Fix javadocs based on recent case consistency change

Commit a40d2447b6f516116135ee7f126579771ba98a2c made the
case consistently "as for the beginning of a sentence".
This updates the docs to reflect that. Previously the
result depended on the string returned (e.g. "Tomorrow"
was capitalized in English) and the casing varied
within and between locales.

Bug: 20247811
Change-Id: If4c6b3a13f61bd0cb64c82fc4c96d053130ae4c8