Change google-http-client version from SNAPSHOT now that 1.21.0 is out.
Change google-http-client version from SNAPSHOT now that 1.21.0 is out.

Related to #650.

ksthesis/gatk,magicDGS/gatk,ksthesis/gatk,frank-y-liu/gatk,magicDGS/gatk,broadinstitute/hellbender,frank-y-liu/gatk,magicDGS/gatk,magicDGS/gatk,broadinstitute/hellbender,ksthesis/gatk,broadinstitute/hellbender,broadinstitute/hellbender,magicDGS/gatk,frank-y-liu/gatk,frank-y-liu/gatk,broadinstitute/hellbender,frank-y-liu/gatk,frank-y-liu/gatk,broadinstitute/hellbender,ksthesis/gatk,ksthesis/gatk,ksthesis/gatk,magicDGS/gatk