Making requirements tighter for "stable" packages in 0.26.1 release. (g…

…oogleapis#3586)

Making requirements tighter for "stable" packages in 0.25.1 release. (g…

…oogleapis#3584)

Making requirements tighter for "stable" packages in error reporting …

…0.25.1 release. (googleapis#3588)

Making requirements tighter for "stable" packages in error reporting …

…0.24.3 release. (googleapis#3587)

Tag umbrella 0.26.0 release.

Tag vision-0.25.0 release.

Tag translate-0.25.0 release.

Tag storage-1.2.0 release.

Tag speech-0.26.0 release.

Prep spanner-0.25.0 release.