s2i/venv: Add enough packages to build non-wheel matplotlib

Eventually we should probably switch to a 2 stage build, but until
then this is good enough

repo2docker/detectors.py

@@ -140,8 +140,8 @@ class PythonBuildPack(S2IBuildPack):
     """Build Pack for installing from a pip requirements.txt using S2I"""
     name = Unicode('python-pip')
     runtime_builder_map = Dict({
-        'python-2.7': 'jupyterhub/singleuser-builder-venv-2.7:v0.2.0',
-        'python-3.5': 'jupyterhub/singleuser-builder-venv-3.5:v0.2.0',
+        'python-2.7': 'jupyterhub/singleuser-builder-venv-2.7:v0.2.1',
+        'python-3.5': 'jupyterhub/singleuser-builder-venv-3.5:v0.2.1',
     })
 
     runtime = Unicode(

s2i-builders/venv/Dockerfile

@@ -8,9 +8,14 @@ ENV APP_DIR /srv/app
 ENV PATH ${APP_DIR}/venv/bin:$PATH
 
 RUN apt-get update && \
-    apt-get install --yes --no-install-recommends \
+    apt-get install --yes \
             python3 \
             python3-venv \
+            python3-dev \
+            build-essential \
+            pkg-config \
+            libfreetype6-dev \
+            libpng-dev \
             tar \
             git \
             locales && \

s2i-builders/venv/Dockerfile.py2

@@ -8,10 +8,13 @@ ENV APP_DIR /srv/app
 ENV PATH ${APP_DIR}/venv/bin:$PATH
 
 RUN apt-get update && \
-    apt-get install --yes --no-install-recommends \
+    apt-get install --yes \
             python \
             python-dev \
             build-essential \
+            pkg-config \
+            libfreetype6-dev \
+            libpng-dev \
             virtualenv \
             tar \
             git \

s2i-builders/venv/version

@@ -1 +1 @@
-v0.2.0
+v0.2.1