Fix `build-release` example to work on current TravisCI

The Travis UUID has been changed from 1000 to 2000, so now making images
is considerably more annoying than before.

README.md

@@ -87,6 +87,19 @@ deploy:
 
 Next, copy [`build-release`](./examples/build-release) into your project and run `chmod +x build-release`.
 
+Finally, add a `Dockerfile` to perform the actual build:
+
+```rust
+FROM ekidd/rust-musl-builder
+
+# We need to add the source code to the image because `rust-musl-builder`
+# assumes a UID of 1000, but TravisCI has switched to 2000.
+ADD . ./
+RUN sudo chown -R rust:rust .
+
+CMD cargo build --release
+```
+
 When you push a new tag to your project, `build-release` will automatically build new Linux binaries using `rust-musl-builder`, and new Mac binaries with Cargo, and it will upload both to the GitHub releases page for your repository.
 
 For a working example, see [faradayio/cage][cage].

examples/build-release

@@ -16,15 +16,15 @@
 
 set -euo pipefail
 
-rust-musl-builder() {
-    docker run --rm -it -v "$(pwd)":/home/rust/src ekidd/rust-musl-builder "$@"
-}
-
 case `uname -s` in
     Linux)
         echo "Building static binaries using ekidd/rust-musl-builder"
-        rust-musl-builder cargo build --release
-        zip -j "$1"-"$2".zip target/x86_64-unknown-linux-musl/release/"$1"
+        docker build -t build-"$1"-image .
+        docker run -it --name build-"$1" build-"$1"-image
+        docker cp build-"$1":/home/rust/src/target/x86_64-unknown-linux-musl/release/"$1" "$1"
+        docker rm build-"$1"
+        docker rmi build-"$1"-image
+        zip "$1"-"$2".zip "$1"
         ;;
     *)
         echo "Building standard release binaries"