fix(md-input): remove update error for md-placholder

also add sample for input using md-placeholder attribute

sample/src/samples/input/placeholder.html

@@ -0,0 +1,7 @@
+<template>
+  <div>
+    <md-input md-placeholder="placeholder text" md-label="put some text here" md-value.bind="textValue"></md-input><br />
+    You entered: ${textValue}<br />
+    <button md-button="flat: true;" md-waves class="accent-text" click.delegate="setText()">set text to something</button>
+  </div>
+</template>

sample/src/samples/input/placeholder.js

@@ -0,0 +1,6 @@
+export class Placeholder {
+  textValue = '';
+  setText() {
+    this.textValue = 'something';
+  }
+}

sample/src/samples/input/registry.json

@@ -24,6 +24,10 @@
     "icon-prefixes": {
       "route": "icon-prefixes",
       "files": ["html", "js"]
+    },
+    "placeholder": {
+      "route": "placeholder",
+      "files": ["html", "js"]
     }
   }
 }

src/input/input.js

@@ -46,7 +46,7 @@ export class MdInput {
     }
     if (this.mdPlaceholder) {
       this.input.setAttribute('placeholder', this.mdPlaceholder);
-      this.update();
+      this.updateService.update();
     }
   }