Fixed typographic typo.

docs/en/manuals/extensions.md

@@ -199,7 +199,7 @@ platforms:
     armv7-ios:
         context:
             frameworks: ["CoreGraphics", "CFNetwork", "GLKit", "CoreMotion", "MessageUI", "MediaPlayer", "StoreKit", "MobileCoreServices", "AdSupport", "AudioToolbox", "AVFoundation", "CoreGraphics", "CoreMedia", "CoreMotion", "CoreTelephony", "CoreVideo", "Foundation", "GLKit", "JavaScriptCore", "MediaPlayer", "MessageUI", "MobileCoreServices", "OpenGLES", "SafariServices", "StoreKit", "SystemConfiguration", "UIKit", "WebKit"]
-            flags:      ["-stdlib=libc``"]
+            flags:      ["-stdlib=libc++"]
             linkFlags:  ["-ObjC"]
             libs:       ["z", "c++", "sqlite3"]
 ```