Remove minimal versions check now that there are no dependencies

Author: dtolnay

.travis.yml

@@ -11,16 +11,3 @@ rust:
 script:
   - cargo run --manifest-path example/Cargo.toml
   - cargo test --all
-
-matrix:
-  include:
-    - rust: nightly
-      name: Minimal versions
-      before_script:
-        - cargo update -Z minimal-versions --manifest-path example/Cargo.toml
-      script:
-        - cargo check --manifest-path example/Cargo.toml
-    - rust: 1.31.0
-      name: 2015 edition
-      script:
-        - cargo check