Adding force to the failing diesel install.

.travis.yml

@@ -23,7 +23,7 @@ script:
   # Default checks, but fail if anything is detected
   - cargo build
   - cargo clippy -- -D clippy::style -D clippy::correctness -D clippy::complexity -D clippy::perf
-  - cargo install diesel_cli --no-default-features --features postgres
+  - cargo install diesel_cli --no-default-features --features postgres --force
   - diesel migration run
   - cargo test
 env: