use yellow for warnings cause it isnt as scary

before:

![screen shot 2013-07-04 at 6 48 12 pm](https://f.cloud.github.com/assets/39759/751763/a9929c48-e515-11e2-9244-f5087350cb02.png)

after:

![screen shot 2013-07-04 at 6 47 46 pm](https://f.cloud.github.com/assets/39759/751764/afd1dd08-e515-11e2-904e-54a41b9627d2.png)

reasoning: countless times i've seen node newbies think that because of all the red warnings that npm failed