Add an ability to avoid "/-" if no max value is set.

[amanenk]

that would be nice to have an option of having something like below
/ Syncing items... (24, 23 items/min) [1m2s]
instead of
/ Syncing items... (24/-, 23 items/min) [1m2s]

[schollz]

would accept PR

[mcamou]

@schollz I'd like to try my hand at this as part of Hacktoberfest, could you please assign me?

[schollz]

@mcamou done

[mcamou]

@schollz PR here: #205

I looked at #139 but thought that ease of use trumps flexibility, WDYT?