doc install: update links to Windows package
doc install: update links to Windows package

https://twitter.com/METAL_GEAR_mkII/status/584680637937750018

Reported by METAL_GEAR_mkII. Thanks!!!

yoku0825/mroonga,yoku0825/mroonga,yoku0825/mroonga,naoa/mroonga,yoku0825/mroonga,yoku0825/mroonga,naoa/mroonga,naoa/mroonga,mroonga/mroonga,naoa/mroonga,mroonga/mroonga,mroonga/mroonga,naoa/mroonga,naoa/mroonga,yoku0825/mroonga,mroonga/mroonga