Fix concat.sh failure when building copay on Windows.
(and silent? bug in Linux builds - build.js attempts to cd to js/browser subdir, but there is no such directory in the copay project, and concat.sh resides in the project root)
Minor spelling fixes in README.md
Merge pull request #268 from eordano/master

Minor spelling fixes in README.md
Merge pull request #264 from dthorpe/fix_concat.sh

Fix concat.sh failure when building copay on Windows.