Increase build version of numpy

for compatibility with tensorflow.
Fixes bob.ip.tensorflow_extractor#10

bob/devtools/data/conda_build_config.yaml

@@ -72,7 +72,7 @@ pkg_config:
 # we are linking against them. It is best to keep this in sync with:
 # https://github.com/AnacondaRecipes/aggregate/blob/master/conda_build_config.yaml
 numpy:
-  - 1.15.4
+  - 1.16.6
 boost:
   - 1.67.0
 ffmpeg:

[André Anjos]

@amohammadi: this somehow caused the stack to break completely. bob.math is not building anymore on software conflicts (https://gitlab.idiap.ch/bob/bob.nightlies/pipelines/38712). Could you please check? Thx!