Fix broken link to GitHub CONTRIBUTING guide.
Fix broken link to GitHub CONTRIBUTING guide.

synicalsyntax/zulip,andersk/zulip,hackerkid/zulip,shubhamdhama/zulip,showell/zulip,brainwane/zulip,rishig/zulip,timabbott/zulip,eeshangarg/zulip,dhcrzf/zulip,punchagan/zulip,jackrzhang/zulip,hackerkid/zulip,punchagan/zulip,jackrzhang/zulip,rishig/zulip,rishig/zulip,eeshangarg/zulip,kou/zulip,shubhamdhama/zulip,rht/zulip,kou/zulip,tommyip/zulip,eeshangarg/zulip,synicalsyntax/zulip,kou/zulip,tommyip/zulip,dhcrzf/zulip,dhcrzf/zulip,punchagan/zulip,kou/zulip,rht/zulip,andersk/zulip,brainwane/zulip,tommyip/zulip,rishig/zulip,mahim97/zulip,eeshangarg/zulip,kou/zulip,showell/zulip,zulip/zulip,dhcrzf/zulip,hackerkid/zulip,rishig/zulip,jackrzhang/zulip,synicalsyntax/zulip,brainwane/zulip,eeshangarg/zulip,jackrzhang/zulip,timabbott/zulip,timabbott/zulip,tommyip/zulip,zulip/zulip,hackerkid/zulip,zulip/zulip,rht/zulip,timabbott/zulip,mahim97/zulip,brainwane/zulip,rht/zulip,zulip/zulip,brainwane/zulip,hackerkid/zulip,shubhamdhama/zulip,timabbott/zulip,synicalsyntax/zulip,synicalsyntax/zulip,zulip/zulip,jackrzhang/zulip,shubhamdhama/zulip,rht/zulip,rishig/zulip,jackrzhang/zulip,shubhamdhama/zulip,andersk/zulip,hackerkid/zulip,rht/zulip,mahim97/zulip,shubhamdhama/zulip,punchagan/zulip,dhcrzf/zulip,andersk/zulip,showell/zulip,andersk/zulip,zulip/zulip,rishig/zulip,hackerkid/zulip,kou/zulip,synicalsyntax/zulip,tommyip/zulip,shubhamdhama/zulip,jackrzhang/zulip,eeshangarg/zulip,synicalsyntax/zulip,kou/zulip,tommyip/zulip,punchagan/zulip,andersk/zulip,showell/zulip,zulip/zulip,mahim97/zulip,dhcrzf/zulip,brainwane/zulip,timabbott/zulip,punchagan/zulip,mahim97/zulip,mahim97/zulip,showell/zulip,showell/zulip,rht/zulip,tommyip/zulip,eeshangarg/zulip,showell/zulip,dhcrzf/zulip,brainwane/zulip,timabbott/zulip,punchagan/zulip,andersk/zulip