Touch up Node.js and MongoDB examples

- Remove extraneous '-' in sudo note.
- Correct space formatting (minor).
- Simplify instructions for install EPEL and install with yum directly.
- Add `nodejs` to yum install list explicitly to match the comments -- more transparent for new users who might not be clear `npm` package also installs `nodejs`.
- Remove '--noprealloc` from MongoDB example as the option has been depcated since Mongo 2.6 and is now the default behaviour. See: http://docs.mongodb.org/manual/reference/program/mongod/

Signed-off-by: Charles Chan <charleswhchan@users.noreply.github.com>

docs/examples/nodejs_web_app.md

@@ -10,14 +10,11 @@ parent = "smn_applied"
 
 # Dockerizing a Node.js web app
 
-> **Note**: 
-> - **If you don't like sudo** then see [*Giving non-root
->   access*](/installation/binaries/#giving-non-root-access)
+> **Note**: **If you don't like sudo** then see [*Giving non-root
+> access*](/installation/binaries/#giving-non-root-access)
 
-The goal of this example is to show you how you can build your own
-Docker images from a parent image using a `Dockerfile`
-. We will do that by making a simple Node.js hello world web
-application running on CentOS. You can get the full source code at
+In this example, we are going to learn how to build a Docker image to run a
+simple Node.js "hello world" web application on CentOS. You can get the full source code at
 [https://github.com/enokd/docker-node-hello/](https://github.com/enokd/docker-node-hello/).
 
 ## Create Node.js app
@@ -75,16 +72,16 @@ available on the [Docker Hub](https://hub.docker.com/):
 
 Since we're building a Node.js app, you'll have to install Node.js as
 well as npm on your CentOS image. Node.js is required to run your app
-and npm to install your app's dependencies defined in
+and npm is required to install your app's dependencies defined in
 `package.json`. To install the right package for
 CentOS, we'll use the instructions from the [Node.js wiki](
 https://github.com/joyent/node/wiki/Installing-Node.js-
 via-package-manager#rhelcentosscientific-linux-6):
 
-    # Enable EPEL for Node.js
-    RUN     rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
+    # Enable Extra Packages for Enterprise Linux (EPEL) for CentOS
+    RUN     yum install -y epel-release
     # Install Node.js and npm
-    RUN     yum install -y npm
+    RUN     yum install -y nodejs npm
 
 To bundle your app's source code inside the Docker image, use the `COPY`
 instruction:
@@ -97,7 +94,7 @@ Install your app dependencies using the `npm` binary:
     # Install app dependencies
     RUN cd /src; npm install
 
-Your app binds to port `8080` so you'll use the` EXPOSE` instruction to have
+Your app binds to port `8080` so you'll use the `EXPOSE` instruction to have
 it mapped by the `docker` daemon:
 
     EXPOSE  8080
@@ -112,10 +109,10 @@ Your `Dockerfile` should now look like this:
 
     FROM    centos:centos6
 
-    # Enable EPEL for Node.js
-    RUN     rpm -Uvh http://download.fedoraproject.org/pub/epel/6/i386/epel-release-6-8.noarch.rpm
+    # Enable Extra Packages for Enterprise Linux (EPEL) for CentOS
+    RUN     yum install -y epel-release
     # Install Node.js and npm
-    RUN     yum install -y npm
+    RUN     yum install -y nodejs npm
 
     # Bundle app source
     COPY . /src