[FAB-7096] Fix grammar in docs/source/Gerrit/gerrit.rst
[FAB-7096] Fix grammar in docs/source/Gerrit/gerrit.rst

Grammar in some of the headings in docs/source/Gerrit/gerrit.rst was
wrong.

Change-Id: I1a319b4ada43bd2994b127b8613d8cd0b0279255
Signed-off-by: Yi Qing Sim <d7af2c6cd7e2c414b1a3d26fa9d800dd81799771@yiqingsim.net>

ckeyer/fabric,ckeyer/fabric,hyperledger/fabric,manish-sethi/fabric-sidedb,lukehuangch/fabric,muralisrini/fabric,jimthematrix/fabric,manish-sethi/fabric-sidedb,lukehuangch/fabric,xixuejia/fabric,ckeyer/fabric,binhn/fabric,stemlending/fabric,ckeyer/fabric,xixuejia/fabric,lukehuangch/fabric,hyperledger/fabric,lukehuangch/fabric,stemlending/fabric,manish-sethi/fabric,stemlending/fabric,manish-sethi/fabric-sidedb,jimthematrix/fabric,muralisrini/fabric,manish-sethi/fabric-sidedb,lukehuangch/fabric,binhn/fabric,binhn/fabric,ckeyer/fabric,manish-sethi/fabric-sidedb,manish-sethi/fabric-sidedb,xixuejia/fabric,ckeyer/fabric,manish-sethi/fabric-sidedb,stemlending/fabric,muralisrini/fabric,ckeyer/fabric,lukehuangch/fabric,manish-sethi/fabric,lukehuangch/fabric