Update tarpaulin to support the new Cargo.lock format

Unfortunately the published binary no longer works on Travis (it's
linked against a libssl that's missing), probably related to
tarpaulin moving its CI to GitHub Actions. Fortunately, cargo
install no longer requires --force to update an installed binary
crate, so building from source and caching the result is simpler
than it used to be.

.travis.yml

@@ -12,8 +12,7 @@ cache: cargo
 install:
   - rustup component add rustfmt-preview
   - rustfmt --version
-  - curl -fsSL https://github.com/xd009642/tarpaulin/releases/download/0.9.0/cargo-tarpaulin-0.9.0-travis.tar.gz | tar xz
-  - mv cargo-tarpaulin ~/.cargo/bin/
+  - cargo install cargo-tarpaulin --version 0.10.2
 
 before_script:
   - wget https://github.com/Ortham/testing-plugins/archive/1.4.1.tar.gz