Added missing mbed-os/core for requirements.txt

Author: screamerbg

mbed/mbed.py

@@ -1185,6 +1185,7 @@ def get_requirements(self):
         mbed_os_path = self.get_os_dir()
         if mbed_os_path:
             paths.append([mbed_os_path])
+            paths.append([mbed_os_path, 'core'])
         # mbed-os not identified but tools found under cwd/tools
         paths.append([self.path, 'core'])
         # mbed Classic deployed tools