Use 1.28 as minimum Rust version

.travis.yml

@@ -78,19 +78,7 @@ matrix:
 
     # Historical Rust versions
     - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.21.0
+      rust: 1.28.0
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.22.0
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.23.0
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.24.0
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.25.0
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.26.0
-    - env: TARGET=x86_64-unknown-linux-gnu
-      rust: 1.27.0
 
     # WASM support
     - env: TARGET=asmjs-unknown-emscripten USE_CARGO_WEB=true

README.md

@@ -67,7 +67,7 @@ Further examples can be found in the [examples](examples) directory on internati
 
 # Usage
 
-`dtparse` requires a minimum Rust version of 1.21 to build, but is tested on Windows, OSX,
+`dtparse` requires a minimum Rust version of 1.28 to build, but is tested on Windows, OSX,
 BSD, Linux, and WASM. The build is also compiled against the iOS and Android SDK's, but is not
 tested against them.
 

src/lib.rs

@@ -63,7 +63,7 @@
 //!
 //! # Usage
 //!
-//! `dtparse` requires a minimum Rust version of 1.21 to build, but is tested on Windows, OSX,
+//! `dtparse` requires a minimum Rust version of 1.28 to build, but is tested on Windows, OSX,
 //! BSD, Linux, and WASM. The build is also compiled against the iOS and Android SDK's, but is not
 //! tested against them.
 //!

src/tests/tz.rs

@@ -1,4 +1,4 @@
-use crate::parse;
+use parse;
 
 #[test]
 fn est() {