Fix wrong context package and update go to 1.14

[alexshtin]

What changed?
Using correct context package now.

Why?
Wrong context package was used in one file.

How did you test it?
Run tests.

Potential risks
No risks.

[alexshtin]

This package should never be used.

[mindaugasrukas]

Check https://golang.org/cmd/fix/

$ go tool fix -h 2>&1 | grep context
context
	Change imports of golang.org/x/net/context to context

[alexshtin]

Check https://golang.org/cmd/fix/

I will add this tool to our list of checkers. Thanks!