doc: fix spelling in Buffer documentation

Change b.writeUint16LE(0x90ab, 0) to b.writeUInt16LE(0x90ab, 0).

PR-URL: #3226
Reviewed-By: Rich Trott <[email protected]>
Reviewed-By: Evan Lucas <[email protected]>

Author: rodmachen

doc/api/buffer.markdown

@@ -232,7 +232,7 @@ A generalized version of all numeric read methods. Supports up to 48 bits of
 accuracy. For example:
 
     var b = new Buffer(6);
-    b.writeUint16LE(0x90ab, 0);
+    b.writeUInt16LE(0x90ab, 0);
     b.writeUInt32LE(0x12345678, 2);
     b.readUIntLE(0, 6).toString(16);  // Specify 6 bytes (48 bits)
     // output: '1234567890ab'