Fix code snippet (wrong method name) in README.md

[polleyg]

Original code snippet in "Querying data" section:

..while (!queryResponse.jobComplete()) {..

This results in a compile error:

"Cannot resolve method jobComplete()"

The correct method is jobCompleted()

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[polleyg]

I signed it!

[googlebot]

CLAs look good, thanks!

[coveralls]

Coverage remained the same at 83.546% when pulling d884fc0 on polleyg:patch-1 into 3da8747 on GoogleCloudPlatform:master.

[lesv]

@tswast PTAL

[tswast]

Thanks!

[garrettjonesgoogle]

Ack try not to merge things between version updates in the future...