Update required version numbers

Author: Matthias247

.travis.yml

@@ -25,7 +25,7 @@ matrix:
 
     # When updating this, the reminder to update the minimum required version in README.md.
     - name: cargo test (minimum required version)
-      rust: nightly-2019-01-11
+      rust: nightly-2019-02-15
 
     - name: cargo clippy
       rust: nightly

README.md

@@ -39,7 +39,7 @@ Now, you can use futures-rs:
 use futures::future::Future; // Note: It's not `futures_preview`
 ```
 
-The current version of futures-rs requires Rust nightly 2019-01-11 or later.
+The current version of futures-rs requires Rust nightly 2019-02-15 or later.
 
 ### Feature `std`