Bump syn & quote in stdweb-derive

[lukaslueg]

syn and quote was recently bumped to "0.14" and "0.6" for stdweb-internal-macros, which in turn updated proc-macro2 to "0.4" from "0.2". Could you bump to those versions in stdweb-derive as well? There is currently a bug in proc-macro2 that prevents compiling for wasm32 and fixing for stdweb would require that proc-macro2 is on the most recent versions everywhere.

[koute]

Seems simple enough; done!