Repeated occurence of `=` isnt handled correctly

[nhz-io]

minimist doesn't handle correctly:

-a=b=c
{ _: [], a: 'b' }

yargs-parser does handle correctly

-a=b=c
{ _: [], a: 'b=c' }

Spawned from: #2 (comment)

[shadowspawn]

I think there are two bugs in this area of the code. The code is looking for an = but not restricting test to just the start of the argument, then assumes there is only one = when assigning the option value.

So the second bug is with -ab=c the b is getting ignored.

minimist/index.js

Line 152 in 980d7ac

if (/[A-Za-z]/.test(letters[j]) && /=/.test(next)) {

minimist/index.js

Line 153 in 980d7ac

setArg(letters[j], next.split('=')[1], arg);