[2.5] Fixed the proxy-manager version constraint

| Q             | A
| ------------- | ---
| Bug fix?      | no
| New feature?  | no
| BC breaks?    | no
| Deprecations? | no
| Tests pass?   | yes
| Fixed tickets | N/A
| License       | MIT
| Doc PR        | N/A

##### This pull request fixes the `ocramius/proxy-manager` version constraint in the 2.5 branch.

The upcoming `1.0.x` is currently similar enough to `0.5.x` that our tests still pass, and there are no breaking changes planned before the final 1.0.0 release, so the `"~1.0"` move should be safe. Note that there are already 3 beta tags on that repo, so it's pretty stable.

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This accompanies #12779 on the 2.3 branch.