Fix capitalization in parseInt description

Author: jakeboone02

src/lib/es5.d.ts

@@ -12,7 +12,7 @@ declare var Infinity: number;
 declare function eval(x: string): any;
 
 /**
-  * Converts A string to an integer.
+  * Converts a string to an integer.
   * @param s A string to convert into a number.
   * @param radix A value between 2 and 36 that specifies the base of the number in numString.
   * If this argument is not supplied, strings with a prefix of '0x' are considered hexadecimal.