Updated the example version under "Depending on Buildcraft" to 6.1.7.

Decided to update the version under "Depending on Buildcraft to 6.1.7 as that's the latest Buildcraft version available, and 6.0.8 is an old release now.
Merge pull request #2187 from KamranMackey/6.1.x

Updated the example version under "Depending on Buildcraft" to 6.1.7.