CI: re-enable 3.4 build / updated conda-build on appeveyor
[fix conda-build version](https://github.com/pydata/pandas/commit/cfbb24f2c0e33ee221c54fd4944458cb0c6f4e84)

Builds are consecutive, 1 at a time.
[disable 3.4 build](https://github.com/pydata/pandas/commit/7e15923d908a42008fb7fecde58be626277fd82e)
