Replace colon to dash

[inertiave]

Fixed an issue that could not be saved properly if the title included colon.

example case
velog post : [assembly: InternalsVisibleTo(string)]

[cjaewon]

I tested that case, in my macbook, it worked properly well.
If your are using windows, below special characters will not work.
so 7 special characters must be replacing like "-"

 \, /, : ,* ,? ," ,< ,> ,|

I will add 6 cases of replacement,
Thank you for contribution!