fix: fix sphinx errors

Author: majorgreys

docs/installation_quickstart.rst

@@ -42,7 +42,7 @@ variable before starting your application and importing the library:
 
 .. list-table::
    :header-rows: 1
-   :widths: 1 1 2
+   :widths: 1 1 1 2
 
    * - Configuration Variable
      - Configuration Type
@@ -64,7 +64,7 @@ that you can use the Datadog tracer in your OpenTracing-compatible
 applications.
 
 Installation
-^^^^^^^^^^^^
+~~~~~~~~~~~~
 
 Include OpenTracing with ``ddtrace``::
 
@@ -78,7 +78,7 @@ you have the following in ``setup.py``::
     ],
 
 Configuration
-^^^^^^^^^^^^^
+~~~~~~~~~~~~~
 
 The OpenTracing convention for initializing a tracer is to define an
 initialization method that will configure and instantiate a new tracer and

tox.ini

@@ -509,9 +509,13 @@ commands=flake8 .
 basepython=python3.7
 
 [testenv:docs]
-deps = sphinx
-commands = sphinx-build -W -b html docs docs/_build/html
-basepython = python
+commands_pre=
+extras=
+  opentracing
+deps=
+  sphinx
+commands=sphinx-build -W -b html docs docs/_build/html
+basepython=python
 
 # do not use develop mode with celery as running multiple python versions within
 # same job will cause problem for tests that use ddtrace-run