Fix typo when running an unknown simulator

Summary:
Just fixes a typo in an error message when running a simulator that XCode doesn't recognise.
Closes https://github.com/facebook/react-native/pull/11060

Differential Revision: D4220364

Pulled By: mkonicek

fbshipit-source-id: da7b9a529ad8cd77c6e144f4bbf3ea594a9efee4

local-cli/runIOS/runIOS.js

@@ -78,7 +78,7 @@ function runOnSimulator(xcodeProject, args, inferredSchemeName, scheme){
 
     const selectedSimulator = findMatchingSimulator(simulators, args.simulator);
     if (!selectedSimulator) {
-      throw new Error(`Cound't find ${args.simulator} simulator`);
+      throw new Error(`Could not find ${args.simulator} simulator`);
     }
 
     const simulatorFullName = formattedDeviceName(selectedSimulator);