Composer: reference shaarli/netscape-bookmark-parser from Packagist

Composer: reference shaarli/netscape-bookmark-parser from Packagist

Relates to https://github.com/shaarli/Shaarli/pull/607
Relates to https://github.com/shaarli/Shaarli/pull/612
Relates to https://github.com/shaarli/netscape-bookmark-parser/issues/15

Modification:
- reference the "shaarli" vendor repository on Packagist instead of
  overriding the upstream package with an SCM repository

See https://packagist.org/packages/shaarli/netscape-bookmark-parser

Signed-off-by: VirtualTam <virtualtam@flibidi.net>