docs(guide/di): fix headings hierarchy

docs/content/guide/di.ngdoc

@@ -105,17 +105,17 @@ dependencies of `MyController` without the controller ever knowing about the inj
 the best outcome. The application code simply asks for the dependencies it needs, without having to
 deal with the injector. This setup does not break the Law of Demeter.
 
-# Dependency Annotation
+## Dependency Annotation
 
 How does the injector know what service needs to be injected?
 
 The application developer needs to provide annotation information that the injector uses in order
-to resolve the dependencies. Throughout Angular certain API functions are invoked using the
+to resolve the dependencies. Throughout Angular, certain API functions are invoked using the
 injector, as per the API documentation. The injector needs to know what services to inject into
 the function. Below are three equivalent ways of annotating your code with service name
 information. These can be used interchangeably as you see fit and are equivalent.
 
-# Inferring Dependencies
+### Inferring Dependencies
 
 The simplest way to get hold of the dependencies, is to assume that the function parameter names
 are the names of the dependencies.
@@ -134,7 +134,7 @@ While straightforward, this method will not work with JavaScript minifiers/obfus
 rename the method parameter names. This makes this way of annotating only useful for {@link
 http://www.pretotyping.org/ pretotyping}, and demo applications.
 
-# `$inject` Annotation
+### `$inject` Annotation
 
 To allow the minifers to rename the function parameters and still be able to inject right services
 the function needs to be annotated with the `$inject` property. The `$inject` property is an array
@@ -153,7 +153,7 @@ function declaration.
 This method of annotation is useful for controller declarations since it assigns the annotation
 information with the function.
 
-# Inline Annotation
+### Inline Annotation
 
 Sometimes using the `$inject` annotation style is not convenient such as when annotating
 directives.
@@ -189,11 +189,11 @@ For this reason the third annotation style is provided as well.
 Keep in mind that all of the annotation styles are equivalent and can be used anywhere in Angular
 where injection is supported.
 
-# Where can I use DI?
+## Where can I use DI?
 
 DI is pervasive throughout Angular. It is typically used in controllers and factory methods. 
 
-## DI in controllers
+### DI in controllers
 
 Controllers are classes which are responsible for application behavior. The recommended way of 
 declaring controllers is:
@@ -209,7 +209,7 @@ declaring controllers is:
 </pre>
 
 
-## Factory methods
+### Factory methods
 
 Factory methods are responsible for creating most objects in Angular. Examples are directives,
 services, and filters. The factory methods are registered with the module, and the recommended way