Fix code block formatting in README.md (#187)

Author: luangong

README.md

@@ -95,13 +95,15 @@ For Closure imports, `protoc` will generate a single output file
 (`myproto_libs.js` in this example).  The generated file will `goog.provide()`
 all of the types defined in your .proto files.  For example, for the unit
 tests the generated files contain many `goog.provide` statements like:
+
 ```js
-    goog.provide('proto.google.protobuf.DescriptorProto');
-    goog.provide('proto.google.protobuf.DescriptorProto.ExtensionRange');
-    goog.provide('proto.google.protobuf.DescriptorProto.ReservedRange');
-    goog.provide('proto.google.protobuf.EnumDescriptorProto');
-    goog.provide('proto.google.protobuf.EnumOptions');
+goog.provide('proto.google.protobuf.DescriptorProto');
+goog.provide('proto.google.protobuf.DescriptorProto.ExtensionRange');
+goog.provide('proto.google.protobuf.DescriptorProto.ReservedRange');
+goog.provide('proto.google.protobuf.EnumDescriptorProto');
+goog.provide('proto.google.protobuf.EnumOptions');
 ```
+
 The generated code will also `goog.require()` many types in the core library,
 and they will require many types in the Google Closure library.  So make sure
 that your `goog.provide()` / `goog.require()` setup can find all of your
@@ -110,11 +112,13 @@ Google Closure library itself.
 
 Once you've done this, you should be able to import your types with
 statements like:
+
 ```js
-    goog.require('proto.my.package.MyMessage');
+goog.require('proto.my.package.MyMessage');
 
-    var message = proto.my.package.MyMessage();
+var message = proto.my.package.MyMessage();
 ```
+
 If unfamiliar with Closure or its compiler, consider reviewing
 [Closure documentation](https://developers.google.com/closure/library).
 
@@ -137,11 +141,13 @@ to build it first by running:
 
 Once you've done this, you should be able to import your types with
 statements like:
+
 ```js
-    var messages = require('./messages_pb');
+var messages = require('./messages_pb');
 
-    var message = new messages.MyMessage();
+var message = new messages.MyMessage();
 ```
+
 The `--js_out` flag
 -------------------
 
@@ -168,17 +174,19 @@ API
 
 The API is not well-documented yet.  Here is a quick example to give you an
 idea of how the library generally works:
+
 ```js
-    var message = new MyMessage();
+var message = new MyMessage();
 
-    message.setName("John Doe");
-    message.setAge(25);
-    message.setPhoneNumbers(["800-555-1212", "800-555-0000"]);
+message.setName("John Doe");
+message.setAge(25);
+message.setPhoneNumbers(["800-555-1212", "800-555-0000"]);
 
-    // Serializes to a UInt8Array.
-    var bytes = message.serializeBinary();
+// Serializes to a UInt8Array.
+var bytes = message.serializeBinary();
 
-    var message2 = MyMessage.deserializeBinary(bytes);
+var message2 = MyMessage.deserializeBinary(bytes);
 ```
+
 For more examples, see the tests.  You can also look at the generated code
 to see what methods are defined for your generated messages.