Fixes nits in string guide

/cc @huonw 
It does seem to render differently in Chrime:
![cholr](https://cloud.githubusercontent.com/assets/531930/4373304/aadd1e32-432b-11e4-925e-16b190157de1.png)

vs in Firefox:
![ffolr](https://cloud.githubusercontent.com/assets/531930/4373367/119ef7f8-432c-11e4-84cb-abac96a4bbe4.png)

So it seems that it is not related to installed system fonts....