chore(deps): update dependency google-cloud-texttospeech to v2.6.0 (#269)

Co-authored-by: nicain <nicain.seattle@gmail.com>
Co-authored-by: Anthonios Partheniou <partheniou@google.com>

Author: 3 people

packages/google-cloud-translate/samples/snippets/hybrid_glossaries/requirements.txt

@@ -1,3 +1,3 @@
 google-cloud-translate==3.4.1
 google-cloud-vision==2.4.4
-google-cloud-texttospeech==2.5.3
+google-cloud-texttospeech==2.6.0