Fix wercker examples, make static examples less error prone

[chris48s]

I think this is probably the only one currently broken on master, but I just made the exact same mistake and didn't notice it in PR #1927 🤦‍♂️

Fix will look like 64974cb

Clearly the way I've done this is a bit fiddly/error prone. I think I need to add some additional error checking to the base class or better assumptions so it is easier to "fall into the pit of success" 🕳️

[PyvesB]

I noticed something else that doesn't seem like correct behaviour: when clicking on a badge URL on the homepage, the badge that appears in the window is broken, as it tries to render it using the placeholder URL:

[paulmelnikow]

Hmm, what's the expected behavior?

Without having separate fields for the values being filled in, this is a bit tricky.

We could not render a badge until the placeholders are filled in, by searching for colons (which aren't used very often).

The badges that have long had placeholders, like CircleCI, have always had this behavior on that screen.

[PyvesB]

Hmm... I didn't realise it would automatically refresh when you typed. Ignore me.