change type of wrap input

Author: Ales Rechtorik

src/lib/input/input.ts

@@ -269,7 +269,7 @@ export class MdInput implements ControlValueAccessor, AfterContentInit, OnChange
   @Input() autocapitalize: string;
   @Input() cols: string;
   @Input() rows: string;
-  @Input() wrap: string;
+  @Input() wrap: 'hard' | 'soft';
   @Input() @BooleanFieldValue() autofocus: boolean = false;
   @Input() @BooleanFieldValue() disabled: boolean = false;
   @Input() id: string = `md-input-${nextUniqueId++}`;