Allow border to be optional.

[Caesarovich]

Fixes #84

Fix not being able to specify empty strings in borderStyle options.

[Caesarovich]

@sindresorhus I propose this to be 7.0.3

[sindresorhus]

You have to update the readme and types too.

[Caesarovich]

@sindresorhus I'm not really sure what you mean by that. Empty strings are still of type string for TS so it does not change anything regarding the types from my point of view. Please let me know your thoughts.

[sindresorhus]

Your pull request title does not match the pull request description. Optional is not the same as empty string.

[sindresorhus]

This is not actually fixing what was asked in the issue. The issue asked for the borderStyle option to be optional.

We could either allow borderStyle to accept undefined or define a new border style called 'none'.

[Caesarovich]

@sindresorhus I'm more into the 'none' option. I'll work on it asap

[Caesarovich]

@sindresorhus That needs investigation, I cannot replicate the test errors. I'm not sure what it is about.

[sindresorhus]

I will publish an update tomorrow.