Update maintainer policy
Update maintainer policy

Clarify criteria for removing a maintainer to include
prolonged inactivity.

Change-Id: I4289bba1706e6766459b778b223b7d4c74c30c7e
Signed-off-by: Christopher Ferris <b3041279349bcb20974a27fd07c65415cf2b925e@us.ibm.com>

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