LESS version does not compiles with less v4

[ZuBB]

Just so you (and everyone who come) know: less version of your breakpoints does not compile with less v4.

for that unit() calls fix is simple -- wrap math expressions into additional parentheses. but for .bp() call I failed to find a fix

[failed] [1 error]

    ERROR in ./src/frontend/assets/skin/theme.less (./node_modules/css-loader/dist/cjs.js!./node_modules/less-loader/dist/cjs.js!./src/frontend/assets/skin/theme.less)
    Module build failed (from ./node_modules/less-loader/dist/cjs.js):



        .bp(m, {
      ^
    Error evaluating function `unit`: Operation on an invalid type