code: function countSpaces(tokens) {
              const before = tokens.arrow.range[0] - tokens.before.range[1];
              const after = tokens.after.range[0] - tokens.arrow.range[1];
  
              return { before, after };
          }
docs: Count spaces before/after arrow(`=>`) token.
  @param {Object} tokens Tokens before/after arrow.
  @returns {Object} count of space before/after arrow.