Fix argument ordering in error message
Summary:
Before:
```
$ ./config set phabricator.base-uri local.phacility.com:8080
Usage Exception: Config option 'http://' is invalid. The URI must start with https://' or 'phabricator.base-uri'.
```
After:
```
$ ./config set phabricator.base-uri local.phacility.com:8080
Usage Exception: Config option 'phabricator.base-uri' is invalid. The URI must start with http://' or 'https://'.
```
Test Plan: See above
Reviewers: epriestley
Reviewed By: epriestley
Subscribers: Korvin
Differential Revision: https://secure.phabricator.com/D19330