Grouped pinning of upstream packages with bugs.

Collect  conda-build #1046, matplotlib #1077 and requests #1101 downgrades in a pinned file so we can add or revert back packages in a easier way than now...
Maybe a little simpler:
```
PINNED_PKGS="
conda-build 1.7.0
requests <2.4.0
matplotlib <1.4.0
"
for x in $PINNED_PKGS; do echo $x >> /home/travis/miniconda/conda-meta/pinned; done
```