Fix compiler warning: unused variable 'j'

../src/pcsc-client.cc:109:19: warning: unused variable 'j' [-Wunused-variable]
                unsigned int i, j, k, nbReaders;
                                ^
Install the npm package on Debian/Ubuntu

Add the npm package to the list of packages to install.
Merge pull request #5 from LudovicRousseau/master

- remove unused j var
- add npm to dependency list