fix: invalid version of ``pyrsistent`` is breaking install.

Signed-off-by: Valentin Lab <valentin.lab@kalysto.org>

bin/myc-install

@@ -119,6 +119,7 @@ EOF
 apt-get install -y build-essential  </dev/null &&
 pip install wheel==0.33.6 &&
 pip install pip==19.3.1 cffi==1.12.3 subprocess32==3.5.4 texttable==1.6.2 \
+    pyrsistent==0.15.7 \
     git+https://github.com/0k/compose@run_ignore_orphans || exit 1
 ## Bug after updating pip
 hash -d pip || exit 1