title: Python3: Trying to upgrade pip3 in Ubuntu 16.04 but it doesn't update
body: <p>Basically, the title. I want to upgrade pip because I cannot get new packages in python because it is obsolete.</p>
  
  <p>When I try to run <code>pip3 install --upgrade pip</code> from the Ubuntu terminal, this happens:</p>
  
  <pre><code>    Collecting pip
    Using cached pip-9.0.3-py2.py3-none-any.whl
  Installing collected packages: pip
    Found existing installation: pip 9.0.1
      Uninstalling pip-9.0.1:
        Successfully uninstalled pip-9.0.1
    Rolling back uninstall of pip
  Exception:
  Traceback (most recent call last):
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/basecommand.py", line 215, in main
      status = self.run(options, args)
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/commands/install.py", line 342, in run
      prefix=options.prefix_path,
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/req/req_set.py", line 784, in install
      **kwargs
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/req/req_install.py", line 851, in install
      self.move_wheel_files(self.source_dir, root=root, prefix=prefix)
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/req/req_install.py", line 1064, in move_wheel_files
      isolated=self.isolated,
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/wheel.py", line 345, in move_wheel_files
      clobber(source, lib_dir, True)
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/wheel.py", line 316, in clobber
      ensure_dir(destdir)
    File "/home/marcell/.local/lib/python3.5/site-packages/pip/utils/__init__.py", line 83, in ensure_dir
      os.makedirs(path)
    File "/usr/lib/python3.5/os.py", line 241, in makedirs
      mkdir(name, mode)
  PermissionError: [Errno 13] Permission denied: '/usr/local/lib/python3.5/dist-packages/pip'
  You are using pip version 9.0.1, however version 9.0.3 is available.
  You should consider upgrading via the 'pip install --upgrade pip' command.
  </code></pre>
  
  <p>How should I solve this problem? I tried to purge pip and reinstall it,but to no avail.</p>
  
  <p>Edit: Also, tried the upgrade command with pip too, but it didn't seem to work.</p>