Soft links python -> python2 for ndk.sh

This fixes #2.

Dockerfile

@@ -12,6 +12,15 @@ RUN apt update && apt -y install \
 
 COPY ndk.sh .
 
+# ndk.sh relies on Python 2 being the default `python`, but in later versions of
+# Ubuntu, you're meant to target either `python2` or `python3` directly.
+# Additionally the meta package for `python` now points to `python3` by default,
+# so this workaround is necessary.
+#
+# Reference:
+# - https://github.com/rhardih/stand/issues/3
+RUN ln -s /usr/bin/python2 /usr/bin/python
+
 # Download and unzip NDK
 RUN ./ndk.sh