deps: update regex crate

This update brings with it a new feature of the regex crate which will
now use SIMD optimizations automatically at runtime with no necessary
compile time flags. All that's needed is to enable the `unstable` feature.

Other crates, such as bytecount and encoding_rs, are still using the
old-style SIMD support, so we leave the simd-accel and avx-accel features.
However, the binaries we distribute on Github no longer have those
features enabled, which makes them truly portable.

Fixes #135

ci/before_deploy.sh

@@ -8,12 +8,7 @@ set -ex
 
 # Generate artifacts for release
 mk_artifacts() {
-    if is_ssse3_target; then
-        RUSTFLAGS="-C target-feature=+ssse3" \
-        cargo build --target "$TARGET" --release --features simd-accel
-    else
-        cargo build --target "$TARGET" --release
-    fi
+    cargo build --target "$TARGET" --release --features unstable
 }
 
 mk_tarball() {