Add libffi-devel as a compile dependencies, Python 3.7 requires it

docker/build_scripts/build.sh

@@ -11,7 +11,7 @@ MY_DIR=$(dirname "${BASH_SOURCE[0]}")
 # Dependencies for compiling Python that we want to remove from
 # the final image after compiling Python
 # GPG installed to verify signatures on Python source tarballs.
-PYTHON_COMPILE_DEPS="zlib-devel bzip2-devel ncurses-devel sqlite-devel readline-devel tk-devel gdbm-devel db4-devel libpcap-devel xz-devel gpg"
+PYTHON_COMPILE_DEPS="zlib-devel bzip2-devel ncurses-devel sqlite-devel readline-devel tk-devel gdbm-devel db4-devel libpcap-devel xz-devel gpg libffi-devel"
 
 # Libraries that are allowed as part of the manylinux1 profile
 MANYLINUX1_DEPS="glibc-devel libstdc++-devel glib2-devel libX11-devel libXext-devel libXrender-devel  mesa-libGL-devel libICE-devel libSM-devel ncurses-devel"