fix(docs-contributing.rst): fix formatting for code snippet

This patch will fix the formatting errors concerning code snippet,
lines 245 and 256 respectively.
The code snippet is updated to 'shell' to lex it appropriately.

Signed-off-by: Jayanth Dodderi Chidanand <jayanthdodderi.chidanand@arm.com>
Change-Id: I53aefd81da350b6511e7a97b5fee7b0d6f9dde2d
diff --git a/docs/process/contributing.rst b/docs/process/contributing.rst
index a0d0683..aa050da 100644
--- a/docs/process/contributing.rst
+++ b/docs/process/contributing.rst
@@ -242,7 +242,7 @@
 #. For better understanding follow the below specified examples listed in the
    ``tf-cov-make`` script.
 
-.. code:: c
+.. code:: shell
 
     Example 1:
     #Intel
@@ -253,7 +253,7 @@
    under the Intel platform and the build configurations has been added suitably
    to include most of their source files.
 
-.. code:: c
+.. code:: shell
 
     Example 2:
     #Hikey