Fix Squeeze Under 1d Action Case

[xunzhang]

When action is 1 dimension(e.g. for debugging), the current code is incorrect since it squeezes additional action dimension. This PR fixed this issue.

[nikhilbarhate99]

Did you test it with Bipedal Walker env after the commit?

[xunzhang]

Yes, please check out log around 4000 episodes below.

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