Remove tests from built package (#124)

...to prevent the tests to be included in production code.

From "Using find_packages()":
    For simple projects, it’s usually easy enough to manually add
    packages to the packages argument of setup(). However, for very
    large projects (Twisted, PEAK, Zope, Chandler, etc.), it can be a
    big burden to keep the package list updated. That’s what
    setuptools.find_packages() is for.

Read:
https://setuptools.readthedocs.io/en/latest/setuptools.html#using-find-packages

Resolves #123

setup.py

@@ -25,7 +25,7 @@
     author_email='[email protected]',
     description='Engine.IO server',
     long_description=long_description,
-    packages=find_packages(),
+    packages=["engineio"],
     zip_safe=False,
     include_package_data=True,
     platforms='any',