fix install-protobuf script to reject old version

[gfr10598]

Our proto definitions use "oneof" which is relatively new. The script does not currently check the version, so this PR adds version checking, and installs a more recent version if version < 3.1.0.

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This change is 

[coveralls]

Coverage remained the same at 90.123% when pulling 39650b8 on gfr10598:master into a0c9d53 on m-lab:master.

[coveralls]

Coverage remained the same at 90.123% when pulling c1551b6 on gfr10598:master into a0c9d53 on m-lab:master.

[coveralls]

Coverage remained the same at 90.123% when pulling 1d9b312 on gfr10598:master into a0c9d53 on m-lab:master.

[gfr10598]

Obsolete