Update the actions/cache step to v4 (#77)

```
Node.js 16 actions are deprecated. Please update the following actions
to use Node.js 20: actions/cache@v3. For more information see:
https://github.blog/changelog/2023-09-22-github-actions-transitioning-from-node-16-to-node-20/.
```

examples/out/scala.yaml

@@ -7,7 +7,7 @@ jobs:
  steps:
  - uses: "actions/checkout@v2"
  - name: "~/.sbt\n\"~/.cache/coursier\"\n cache"
- uses: "actions/cache@v3"
+ uses: "actions/cache@v4"
  with:
  key: "${{ runner.os }}-sbt-${{ hashFiles('build.sbt', 'project/plugins.sbt', 'project/build.properties', 'project/Dependencies.scala') }}"
  path: |
@@ -36,7 +36,7 @@ jobs:
  steps:
  - uses: "actions/checkout@v2"
  - name: "~/.sbt\n\"~/.cache/coursier\"\n cache"
- uses: "actions/cache@v3"
+ uses: "actions/cache@v4"
  with:
  key: "${{ runner.os }}-sbt-${{ hashFiles('build.sbt', 'project/plugins.sbt', 'project/build.properties', 'project/Dependencies.scala') }}"
  path: |

steps.dhall

@@ -9,7 +9,7 @@
  sha256:8a22d29eea007b2df0c3467dc732b835e46f3daccefba38312d4b4446c50b006
 , actions/cache =
  ./steps/actions/cache.dhall
- sha256:8828d57d24a29354d6be9ca28db540224f89aec12cda593abe1580729e10ebc4
+ sha256:b6d6702a9faa91b3b64f9ac7e84b1f8706a460dd02fcf2e47cbbedb9053e6e96
 , actions/helloWorld =
  ./steps/actions/helloWorld.dhall
  sha256:69bc163d0b30165fb1792c23871a0ad6fade1095517f6b3fa3b834a615f3d2fc

steps/actions/cache.dhall

@@ -22,7 +22,7 @@ in λ(args : { path : Text, key : Text, hashFiles : List Text }) →
 
  in Step::{
  , name = Some "${args.path} cache"
- , uses = Some "actions/cache@v3"
+ , uses = Some "actions/cache@v4"
  , `with` = Some
  ( toMap
  { path = args.path