Align summary values in text email template

Aligning these values in the text email template will make it a little
easier to scan and a little more aesthetically pleasing.

Before example:

```
Deployer: First Last
Application: MyApp
Branch: master
Environment: prod
Time: 01/09/2014 at 03:44 PM PDT
```

After example:

```
Deployer:     First Last
Application:  MyApp
Branch:       master
Environment:  prod
Time:         01/09/2014 at 03:44 PM PDT
```