Fix usage of cross-env in examples

[ericf]

Fixes #855

[bartvanandel]

Unfortunately this change results in breakage on Windows. The whole purpose of cross-env is to make things run across different environments. Adding a path to an executable (/ on unix-like systems, \ on Windows) basically undoes this advantage as the command no longer runs at all:

D:\src\react-intl\examples\async>npm run clean

> react-intl-example-async@1.0.0 clean D:\src\bart\github\react-intl\examples\async
> ../../node_modules/.bin/cross-env ../../node_modules/.bin/rimraf build

'..' is not recognized as an internal or external command,
operable program or batch file.

npm ERR! Windows_NT 10.0.14393
npm ERR! argv "C:\\Program Files\\nodejs\\node.exe" "C:\\Program Files\\nodejs\\node_modules\\npm\\bin\\npm-cli.js" "run" "clean"
[... etc]

BTW I'm not sure what the proper fix would be here, don't shoot the messenger please! I suppose adding cross-env (and maybe friends) to the package.json file inside the examples would help, but I guess you don't want the examples to behave like actual packages and just use the package.json file for the convenience of being able to run scripts?

[JeremieLeblanc]

Will the examples ever be fixed on windows?