[v2.0.1] class name cannot be only numbers

[aleclarson]

~/pug-cli/node_modules/pug-lexer/index.js:60
    throw err;
    ^

Error: test.pug:58:5
    56|       +another(abc=123, bcd='lol')
    57| 
  > 58|     .98349 class name only numbers
------------^
    59|     ._[invalid character in class name should result in it and text following be considered text
    60| 
    61|     //  some html comment

Class names must contain at least one letter or underscore.
    at makeError (~/pug-cli/node_modules/pug-error/index.js:32:13)
    at Lexer.error (~/pug-cli/node_modules/pug-lexer/index.js:59:15)
    at Lexer.className (~/pug-cli/node_modules/pug-lexer/index.js:445:12)
    at Lexer.callLexerFunction (~/pug-cli/node_modules/pug-lexer/index.js:1456:23)
    at Lexer.advance (~/pug-cli/node_modules/pug-lexer/index.js:1492:15)
    at Lexer.callLexerFunction (~/pug-cli/node_modules/pug-lexer/index.js:1456:23)
    at Lexer.getTokens (~/pug-cli/node_modules/pug-lexer/index.js:1512:12)
    at lex (~/pug-cli/node_modules/pug-lexer/index.js:12:42)
    at Object.lex (~/pug-cli/node_modules/pug/lib/index.js:99:27)
    at Function.loadString [as string] (~/pug-cli/node_modules/pug-load/index.js:44:24)