Correction on default value for config file (benoitc#2408)

Running gunicorn project.app while having a file called gunicorn.conf.py
in the current directory will read configuration from that file and actually fail
if the file raises an exception.

docs/source/settings.rst

@@ -29,7 +29,7 @@ config
 ~~~~~~
 
 * ``-c CONFIG, --config CONFIG``
-* ``None``
+* ``./gunicorn.conf.py``
 
 The Gunicorn config file.
 
@@ -38,6 +38,9 @@ A string of the form ``PATH``, ``file:PATH``, or ``python:MODULE_NAME``.
 Only has an effect when specified on the command line or as part of an
 application specific configuration.
 
+By default, a file named ``gunicorn.conf.py`` will be read from the same
+directory where gunicorn is being run.
+
 .. versionchanged:: 19.4
    Loading the config from a Python module requires the ``python:``
    prefix.

gunicorn/config.py

@@ -546,7 +546,7 @@ class ConfigFile(Setting):
     cli = ["-c", "--config"]
     meta = "CONFIG"
     validator = validate_string
-    default = None
+    default = "./gunicorn.conf.py"
     desc = """\
         The Gunicorn config file.
 
@@ -555,6 +555,9 @@ class ConfigFile(Setting):
         Only has an effect when specified on the command line or as part of an
         application specific configuration.
 
+        By default, a file named ``gunicorn.conf.py`` will be read from the same
+        directory where gunicorn is being run.
+
         .. versionchanged:: 19.4
            Loading the config from a Python module requires the ``python:``
            prefix.