Remove zip_safe from install.rst documentation

`zip_safe` is obsolete per:
https://setuptools.pypa.io/en/latest/deprecated/zip_safe.html

In summary:
> It is very unlikely that the values of zip_safe will affect modern deployments that use pip for installing packages. Moreover, new users of setuptools should not attempt to create egg files using the deprecated build_egg command. Therefore, this flag is considered obsolete.

docs/tutorial/install.rst

@@ -41,7 +41,6 @@ to it.
         version='1.0.0',
         packages=find_packages(),
         include_package_data=True,
-        zip_safe=False,
         install_requires=[
             'flask',
         ],