96b Nitrogen Board: pyocd-flashtool syntax update

* 'pyOCD-flashtool -l' command syntax rectified as 'pyocd-flashtool -l',
 fixes issue#39

Signed-off-by: Arul Kumaran <arulkumaran.devarajan@huawei.com>

docs/hardware-support/boards/96b-nitrogen.rst

@@ -90,7 +90,7 @@ pyOCD is an open source Python package for programming and debugging Arm Cortex-
 
 .. code-block:: console
 
-   $ pyOCD-flashtool -l
+   $ pyocd-flashtool -l
 
 .. note::