Fixes for parsing JSX tokens array

With `tokens` option enabled, esprima-fb returns incorrect array of tokens in `ast.tokens` property in following ways:

1. Duplicate `XJSText` tokens appear due to double-peeking next token into tokens array by both `expect()` in `parseXJSOpeningElement()` and `peek()` in `parseXJSElement()`.
2. Whitespaces in `<Tag> a </Tag>` were ignored and returned as pure `'a'` literal inside of `XJSText` element; this also caused children array of `<Tag> </Tag>` to be empty when `tokens` option was enabled.

Both bugs are fixed and regression test added.

Also:

1. Ignored `node_modules` folder.
2. Added running JSX tests in browser.
3. Changed versions in code to same as in package.json (required for tests).