scripts: More explicit error in west_commands for NRF flashing

Instead of suggesting a python dep is missing, tell the user intelhex is
missing.

Signed-off-by: Félix Piédallu <felix@piedallu.me>

scripts/west_commands/runners/nrf_common.py

@@ -443,7 +443,7 @@ class NrfBinaryRunner(ZephyrBinaryRunner):
 
         self.ensure_output('hex')
         if IntelHex is None:
-            raise RuntimeError('one or more Python dependencies were missing; '
+            raise RuntimeError('Python dependency intelhex was missing; '
                                'see the getting started guide for details on '
                                'how to fix')
         self.hex_contents = IntelHex()