[travis] Update travis configuration to run on stable Rust.

.travis.yml

@@ -17,7 +17,7 @@ env:
     - secure: dIur06XYomBukvYR0aymt8D6YQpTGYvejZtInEmjOdnWziJJZmQ+HuTXMnXrrwFEFSC21uQfgBwhlItwcEzFu1ydx1LlxuUZh8sFjTFFrCWo3hRpyb4JGCAwoNvUZ1/d7MwHjGxjzFtMvnVPyo/wHlE2xgkWHZqmJfDgGkkpBuk=
 
 language: rust
-rust: nightly
+rust: stable
 script:
   - cargo build
   - cargo test

README.md

@@ -6,7 +6,7 @@ Constraint Programming Library
 [travis-image]: https://travis-ci.org/ptal/pcp.png
 [travis]: https://travis-ci.org/ptal/pcp
 
-PCP is a library in *stable Rust* to model constraint satisfaction problems (CSPs) in the constraint programming paradigm.
+PCP is a library to model constraint satisfaction problems (CSPs) in the constraint programming paradigm.
 Constraint programming is a paradigm for expressing problems in terms of mathematical relations, called constraints, over variables (e.g. `x > y`).
 Constraints are an intuitive approach to naturally describe many real-world problems which initially emerged as a subfield of artificial intelligence and operational research.
 The flagship applications in constraint programming encompass scheduling, configuration and vehicles routing problems.
@@ -16,6 +16,8 @@ It is a programming paradigm in its own right and being able to program in Rust
 This is why I strongly recommend the class [Basic Modeling for Discrete Optimization](https://www.coursera.org/learn/basic-modeling) for those who wants to learn this paradigm.
 Meanwhile you can already look at the [documentation](https://docs.rs/crate/pcp/1.0.0) for a running example.
 
+PCP compiles on the *stable Rust* channel.
+
 ### References
 
 Existing libraries are an invaluable source of inspiration: