case 109 incorrect in keysym.js file should be case 173

[TclHttpd]

In the keysym.js file in the include directory of websockify, the minus sign for Mozilla is case 109. This is in fact is the minus sign for the numerical keypad. Changing it to case 173 gives the intended key on the keyboard and makes it the same as Chrome and IE.

[DirectXMan12]

Thanks for the bug report. We actually sync keysym.js from noVNC, which has a completely updated version of keysym.js. We should be syncing that in soon.