In /usr/bin/gacutil line 2:
exec /usr/bin/mono $MONO_OPTIONS /usr/lib/mono/4.5/gacutil.exe "$@"
                   ^-----------^ SC2086: Double quote to prevent globbing and word splitting.

Did you mean: 
exec /usr/bin/mono "$MONO_OPTIONS" /usr/lib/mono/4.5/gacutil.exe "$@"

For more information:
  https://www.shellcheck.net/wiki/SC2086 -- Double quote to prevent globbing ...