Need the stretch-backports version of debootstrap's database

Dockerfile

@@ -4,22 +4,27 @@ FROM cryptech-builder:base
 # stuff is much more likely to change than the XiLinx tools, so we put
 # it at the end of the build where we can use normal Docker tooling.
 
-RUN apt-get update && \
+RUN sed -i -E \
+	-e '/stretch-backports/d' \
+	-e '/ stretch /{; h; s/ stretch / stretch-backports /; x; G; }' \
+	/etc/apt/sources.list && \
+    apt-get update && \
+    apt-get upgrade --with-new-pkgs -y && \
     apt-get install -y \
-	    avr-libc \
-	    binutils-avr \
-	    debootstrap \
-	    distro-info-data \
-	    gcc-arm-none-eabi \
-	    gcc-avr \
-	    git \
-	    pbuilder \
-	    python-crypto \
-	    python-serial \
-	    python-yaml \
-	    reprepro \
-	    ubuntu-archive-keyring \
-	    ubuntu-dev-tools
+	avr-libc \
+	binutils-avr \
+	debootstrap/stretch-backports \
+	distro-info-data \
+	gcc-arm-none-eabi \
+	gcc-avr \
+	git \
+	pbuilder \
+	python-crypto \
+	python-serial \
+	python-yaml \
+	reprepro \
+	ubuntu-archive-keyring \
+	ubuntu-dev-tools
 
 USER	builder
 WORKDIR /home/builder