…es in preparation for python3

  :not(kbd) > kbd,
 ^
      Property "not" must be followed by a ':'
      in /project/src/sass/_theme_rst.sass (line 518, column 3)
    at /project/node_modules/webpack/lib/NormalModule.js:316:20
    at /project/node_modules/loader-runner/lib/LoaderRunner.js:367:11
    at /project/node_modules/loader-runner/lib/LoaderRunner.js:233:18
    at context.callback (/project/node_modules/loader-runner/lib/LoaderRunner.js:111:13)
    at Object.callback (/project/node_modules/sass-loader/dist/index.js:89:7)
    at Object.done [as callback] (/project/node_modules/neo-async/async.js:8069:18)
    at options.error (/project/node_modules/node-sass/lib/index.js:294:32)
 @ multi ./src/theme.js ./src/sass/theme.sass theme[1]
Child mini-css-extract-plugin node_modules/css-loader/dist/cjs.js!node_modules/sass-loader/dist/cjs.js??ref--5-2!src/sass/badge_only.sass:
    Entrypoint mini-css-extract-plugin = *
    [0] ./node_modules/css-loader/dist/cjs.js!./node_modules/sass-loader/dist/cjs.js??ref--5-2!./src/sass/badge_only.sass 4.69 KiB {0} [built]
        + 7 hidden modules
Child mini-css-extract-plugin node_modules/css-loader/dist/cjs.js!node_modules/sass-loader/dist/cjs.js??ref--5-2!src/sass/theme.sass:
    Entrypoint mini-css-extract-plugin = *
    [0] ./node_modules/css-loader/dist/cjs.js!./node_modules/sass-loader/dist/cjs.js??ref--5-2!./src/sass/theme.sass 227 bytes {0} [built] [failed] [1 error]

    ERROR in ./src/sass/theme.sass (./node_modules/css-loader/dist/cjs.js!./node_modules/sass-loader/dist/cjs.js??ref--5-2!./src/sass/theme.sass)
    Module build failed (from ./node_modules/sass-loader/dist/cjs.js):

      :not(kbd) > kbd,
     ^
          Property "not" must be followed by a ':'
          in /project/src/sass/_theme_rst.sass (line 518, column 3)

…t running the build

… we’re setting up an environment that is isolated from the CI (or primary) container, then using the remote host’s Docker Engine."

Build with Node 14 installed through orbs.

Fixes readthedocs#1275

This introduced syntax errors that were not picked up in review, the
`:not()` psuedo selector can't lead a selector in SASS.