Fix references to removed 'hello_world' example.

README.md

@@ -61,7 +61,7 @@ example can be compiled and run with Cargo. For instance, the following sequence
 of commands builds and runs the `Hello, world!` example:
 
 ```sh
-cd examples/hello_world
+cd examples/hello
 cargo run
 ```
 

site/guide/1-quickstart.md

@@ -9,13 +9,13 @@ started](../getting-started) section.
 
 The absolute fastest way to start experimenting with Rocket is to clone the
 Rocket repository and run the included examples in the `examples/` directory.
-For instance, the following set of commands runs the `hello_world` example:
+For instance, the following set of commands runs the `hello` example:
 
 ```sh
 git clone https://github.com/SergioBenitez/Rocket
 cd Rocket
 git checkout master
-cd examples/hello_world
+cd examples/hello
 cargo run
 ```
 

site/guide/8-testing.md

@@ -299,7 +299,7 @@ During compilation, you should see output like:
 
 ```rust,ignore
 note: emitting Rocket code generation debug output
-  --> examples/hello_world/src/main.rs:14:1
+  --> examples/hello/src/main.rs:14:1
    |
 14 | #[get("/world")]
    | ^^^^^^^^^^^^^^^^