R1:db20c74044cb

Add a missing (string) cast to repository.query

Summary: The method returns a PhutilURI object, which json_encode() encodes as "{}" since all the properties are private.

Test Plan:
Examined the output of "repository.query" more carefully:

"0" : {
"name" : "Phabricator",
"callsign" : "P",
"vcs" : "git",
"uri" : "http:\/\/local.aphront.com:8080\/diffusion\/P\/",
"remoteURI" : "git:\/\/github.com\/facebook\/phabricator.git",
"tracking" : true
},

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