Fix spelling issue in hroller.rst
Fix spelling issue in hroller.rst

'explicitly' was spelled the wrong way

Signed-off-by: Benjamin Kerensa <531a2364218795bb839b6fb7fe678ac086b364e0@ubuntu.com>
Signed-off-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>
Reviewed-by: Guido Trotter <f62ca4d5358bdaeef0e50e57f9f7e231de63727e@google.com>

apyrgio/snf-ganeti,grnet/snf-ganeti,yiannist/ganeti,ganeti-github-testing/ganeti-test-1,andir/ganeti,mbakke/ganeti,leshchevds/ganeti,bitemyapp/ganeti,ganeti/ganeti,leshchevds/ganeti,yiannist/ganeti,apyrgio/snf-ganeti,dimara/ganeti,onponomarev/ganeti,ganeti/ganeti,leshchevds/ganeti,andir/ganeti,ganeti/ganeti,yiannist/ganeti,bitemyapp/ganeti,apyrgio/ganeti,grnet/snf-ganeti,apyrgio/ganeti,dimara/ganeti,mbakke/ganeti,mbakke/ganeti,ganeti-github-testing/ganeti-test-1,onponomarev/ganeti,andir/ganeti