Update installation.rst
Update installation.rst

On Windows, it's the batchbin directory (which contains casperjs.bat) which needs to be added to the PATH, not bin.
casperjs/casperjs,istr/casperjs,hlr1983/casperjs,jefleponot/casperjs,istr/casperjs,jefleponot/casperjs,istr/casperjs,istr/casperjs,n1k0/casperjs,casperjs/casperjs,casperjs/casperjs,mickaelandrieu/casperjs,n1k0/casperjs,casperjs/casperjs,hlr1983/casperjs,jefleponot/casperjs,n1k0/casperjs,jefleponot/casperjs,mickaelandrieu/casperjs,istr/casperjs,mickaelandrieu/casperjs,hlr1983/casperjs,mickaelandrieu/casperjs,casperjs/casperjs,hlr1983/casperjs,mickaelandrieu/casperjs,jefleponot/casperjs,jefleponot/casperjs,casperjs/casperjs,hlr1983/casperjs,n1k0/casperjs,n1k0/casperjs,istr/casperjs,n1k0/casperjs,hlr1983/casperjs,mickaelandrieu/casperjs