Replace --fulltrace with --full-trace in doc

Since 'py.test --help' shows --full-trace as an option (and not --fulltrace)
even though both forms are accepted I assume --full-trace is the preferred form
and should therefore be used in the documentation.

doc/en/example/simple.rst

@@ -201,7 +201,7 @@ Example::
 
 The ``__tracebackhide__`` setting influences ``pytest`` showing
 of tracebacks: the ``checkconfig`` function will not be shown
-unless the ``--fulltrace`` command line option is specified.
+unless the ``--full-trace`` command line option is specified.
 Let's run our little function::
 
     $ py.test -q test_checkconfig.py

doc/en/test/plugin/terminal.rst

@@ -22,7 +22,7 @@ command line options
     (deprecated, use -r)
 ``--tb=style``
     traceback print mode (long/short/line/no).
-``--fulltrace``
+``--full-trace``
     don't cut any tracebacks (default is to cut).
 ``--fixtures``
     show available function arguments, sorted by plugin