Update link to GitHub project

Thanks for your great product.

I'm a new to vert.x, yesterday I read official web site and found that some page still link to old GitHub pages. This MR tries to update them to the latest one.

Note that we still have some dead-links, sorry but I cannot find where is the latest one of following examples:

* https://github.com/vert-x/vert.x/tree/master/vertx-examples/src/main/groovy
* https://github.com/vert-x/vert.x/tree/master/vertx-examples/src/main/javascript
* https://github.com/vert-x/vert.x/tree/master/vertx-examples/src/main/ruby

This MR also contains fix for a typo: `\tmp` -> `/tmp`. This is similar to #40 but fixes all files in this project.

Thanks in advance,
Kengo TODA