Install nasm in the docker image cross compiling for *-windows-gnu

ci/Dockerfile-mingw

@@ -2,5 +2,5 @@ FROM ubuntu:16.04
 
 RUN apt-get update
 RUN apt-get install -y --no-install-recommends \
-  gcc ca-certificates make libc6-dev \
+  gcc ca-certificates make nasm libc6-dev \
   gcc-mingw-w64-x86-64 libz-mingw-w64-dev

ci/run.sh

@@ -6,18 +6,7 @@ cargo test --target $TARGET --no-run
 # First test with no extra protocols enabled.
 cargo test --target $TARGET --no-run --features static-curl
 # Then with rustls TLS backend.
-#
-# Note: Cross-compiling rustls on windows doesn't work due to requiring some
-# NASM build stuff in aws_lc_rs, which may soon be fixed by
-# https://github.com/aws/aws-lc-rs/pull/528.
-#
-# Compiling on i686-windows requires nasm to be installed (other platforms
-# have pre-compiled object files), which is just slightly too much
-# inconvenience for me.
-if [ "$TARGET" != "x86_64-pc-windows-gnu" ] && [ "$TARGET" != "i686-pc-windows-msvc" ]
-then
-    cargo test --target $TARGET --no-run --features rustls,static-curl
-fi
+cargo test --target $TARGET --no-run --features rustls,static-curl
 # Then with all extra protocols enabled.
 cargo test --target $TARGET --no-run --features static-curl,protocol-ftp,ntlm
 if [ -z "$NO_RUN" ]; then