Add built/test workflow & badge, drop travis.

Author: brndnmtthws

.github/workflows/build-and-test.yml

@@ -0,0 +1,17 @@
+on: [push]
+
+name: CI
+
+jobs:
+  build_and_test:
+    name: Rust project
+    runs-on: ubuntu-latest
+    steps:
+      - uses: actions/checkout@v2
+      - uses: actions-rs/toolchain@v1
+        with:
+          toolchain: stable
+      - uses: actions-rs/cargo@v1
+        with:
+          command: build
+          args: --release --all-features

.travis.yml

@@ -1,4 +1,4 @@
-[![Build Status](https://travis-ci.org/brndnmtthws/cracking-the-coding-interview-rust.svg?branch=master)](https://travis-ci.org/brndnmtthws/cracking-the-coding-interview-rust) [![Dependabot Status](https://api.dependabot.com/badges/status?host=github&repo=brndnmtthws/cracking-the-coding-interview-rust)](https://dependabot.com) [![Coverage Status](https://coveralls.io/repos/github/brndnmtthws/cracking-the-coding-interview-rust/badge.svg?branch=master)](https://coveralls.io/github/brndnmtthws/cracking-the-coding-interview-rust?branch=master)
+![Build status](https://github.com/brndnmtthws/cracking-the-coding-interview-rust/actions/workflows/build-and-test.yml/badge.svg) [![Dependabot Status](https://api.dependabot.com/badges/status?host=github&repo=brndnmtthws/cracking-the-coding-interview-rust)](https://dependabot.com) [![Coverage Status](https://coveralls.io/repos/github/brndnmtthws/cracking-the-coding-interview-rust/badge.svg?branch=master)](https://coveralls.io/github/brndnmtthws/cracking-the-coding-interview-rust?branch=master)
 
 # Cracking the Coding Interview with Rust