setup.py: bump Pygments minimum version to 2.2.0

With pygments < 2.2.0, the markup_renderer doctest fails:

> python -m doctest kallithea/lib/markup_renderer.py
**********************************************************************
File "kallithea/lib/markup_renderer.py", line 184, in markup_renderer.MarkupRenderer.markdown
Failed example:
    print MarkupRenderer.markdown('''
        #!/bin/bash
        echo "hello"
    ''')
Expected:
    <table class="code-highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre>1
    2</pre></div></td><td class="code"><div class="code-highlight"><pre><span></span><span class="ch">#!/bin/bash</span>
    <span class="nb">echo</span> <span class="s2">"hello"</span>
    </pre></div>
    </td></tr></table>
Got:
    <table class="code-highlighttable"><tr><td class="linenos"><div class="linenodiv"><pre>1
    2</pre></div></td><td class="code"><div class="code-highlight"><pre><span class="ch">#!/bin/bash</span>
    <span class="nb">echo</span> <span class="s2">"hello"</span>
    </pre></div>
    </td></tr></table>
**********************************************************************


To avoid having to manage multiple outputs from multiple versions, just bump
the lower version.

pygments 2.2.0 was released on Jan 22, 2017.

setup.py

@@ -53,7 +53,7 b' requirements = ['
     "FormEncode >= 1.3.0, < 1.4",
     "SQLAlchemy >= 1.1, < 1.4",
     "Mako >= 0.9.0, < 1.1",
-    "Pygments >= 2.0, < 2.5",
+    "Pygments >= 2.2.0, < 2.5",
     "Whoosh >= 2.5.0, < 2.8",
     "celery >= 3.1, < 4.0", # TODO: celery 4 doesn't work
     "Babel >= 1.3, < 2.8",