Release share v0.25.1 (2021-04-06)

Set the minimum Go version to 1.16

Commit 4cdd6b01c1 "http: add method to generate standard HTTP request
on Client" use the io.NopCloser thats only available in Go 1.16.  Either
we move backward by replacing it with ioutil.NopCloser or we move forward
by setting the minimum Go version to 1.16.

We choose to move forward.
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