npm: don't publish tests in the npm package

Given that metarhia/jstp#158 has introduced
quite a massive chunk of test fixtures, it is better to avoid including
tests with the npm package.  At this point it saves 632 KB of disk
space.

PR-URL: metarhia/jstp#159
Reviewed-By: Denys Otrishko <shishugi@gmail.com>
Reviewed-By: Dmytro Nechai <nechaido@gmail.com>
Reviewed-By: Mykola Bilochub <nbelochub@gmail.com>

.npmignore

@@ -23,3 +23,6 @@ mkdocs.yml
 
 # Examples
 examples/
+
+# Tests
+test/