'Unknown word' for valid LESS

[eddie-dunn]

• Node Version: v8.13.0
• NPM Version: 6.4.1
• postcss Version: 7.0.6
• postcss-less Version: 3.1.0

LESS

// web/test.less
.test {
	.foo( {
		width: calc(~"100% + 1px");
	} );
}

Errors

When running stylelint "web/test.less"

web/test.less
 4:4  ✖  Unknown word   CssSyntaxError

error Command failed with exit code 2)

Expected Behavior

No error.

Actual Behavior

Error.

How can we reproduce the behavior?

See above.

[shellscape]

Happy to review a PR that resolves this.