Log Message:
mlterm: update to 3.8.7.

Changes noted in doc/en/ReleaseNote:

ver 3.8.7
* Support sixel graphics extension and option1 of
  https://github.com/kmiya-culti/RLogin/issues/22#issue-341758598
* Support Cygwin/x86_64.
* Support PS2 mouse and PC98 bus mouse on FreeBSD 4.x or before.
* Support iOS/Cocoa Touch. (see doc/en/README.cocoatouch)
* Support scrolling by flick on Android and iOS.
* Update unicode property table (generated from UnicodeData.txt and
  EastAsianWidth.txt) to version 11.0.0.
* Add "autoscroll" to OSC 5379.
* Long press at the lower right corner instead of the entire screen shows
  context menu.
* Change the maximum number of sixel graphics palette colors from 256 to 1024.
* Bug fixes:
  Fix segfault of mlconfig when GTK_IM_MODULE=uim.
  Fix wrong XSizeHints which causes unexpected resizing.