Improve grammar of one sentence

Signed-off-by: Philipp Ahmann <2428012+pahmann@users.noreply.github.com>

Author: pahmann

process/process_areas/verification/guidance/verification_methods.rst

@@ -178,7 +178,7 @@ Derivation Techniques
    * :ref:`Equivalence Classes <ver_equivalence>`
    * :ref:`Fuzzy Testing <ver_fuzzy>`
 
-   Note: more than a derivation technique can be used in a single test case
+   Note: more than one derivation technique can be used in a single test case
 
 .. _ver_boundary: