Merge pull request #2502 from zhongsp/master

doc: fix typo 'BankAccount'

Author: mhegazy

doc/TypeScript Language Specification (Change Markup).docx

@@ -545,7 +545,7 @@ class CheckingAccount extends BankAccount {
 }
 ```
 
-In this example, the class 'CheckingAccount' *derives* from class 'BankAccount'. The constructor for 'CheckingAccount' calls the constructor for class 'BankAccount' using the 'super' keyword. In the emitted JavaScript code, the prototype of 'CheckingAccount' will chain to the prototype of 'BankingAccount'. 
+In this example, the class 'CheckingAccount' *derives* from class 'BankAccount'. The constructor for 'CheckingAccount' calls the constructor for class 'BankAccount' using the 'super' keyword. In the emitted JavaScript code, the prototype of 'CheckingAccount' will chain to the prototype of 'BankAccount'. 
 
 TypeScript classes may also specify static members. Static class members become properties of the class constructor.