Update precache help

packages/flutter_tools/lib/src/commands/precache.dart

@@ -16,21 +16,21 @@ class PrecacheCommand extends FlutterCommand {
     argParser.addFlag('force', abbr: 'f', negatable: false,
         help: 'Force downloading of artifacts.');
     argParser.addFlag('android', negatable: true, defaultsTo: true,
-        help: 'Precache artifacts for Android development');
+        help: 'Precache artifacts for Android development.');
     argParser.addFlag('ios', negatable: true, defaultsTo: true,
-        help: 'Precache artifacts for iOS developemnt');
+        help: 'Precache artifacts for iOS development.');
     argParser.addFlag('web', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for web development');
+        help: 'Precache artifacts for web development.');
     argParser.addFlag('linux', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for linux desktop development');
+        help: 'Precache artifacts for Linux desktop development.');
     argParser.addFlag('windows', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for windows desktop development');
+        help: 'Precache artifacts for Windows desktop development.');
     argParser.addFlag('macos', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for macOS desktop development');
+        help: 'Precache artifacts for macOS desktop development.');
     argParser.addFlag('fuchsia', negatable: true, defaultsTo: false,
-        help: 'Precache artifacts for Fuchsia development');
+        help: 'Precache artifacts for Fuchsia development.');
     argParser.addFlag('universal', negatable: true, defaultsTo: true,
-        help: 'Precache artifacts required for all developments');
+        help: 'Precache artifacts required for any development platform.');
   }
 
   @override