Merge pull request #1478 from kraktus/dev-deps

Update `Development dependencies` page.

src/testing/dev_dependencies.md

@@ -5,30 +5,26 @@ or benchmarks) only. Such dependencies are added to `Cargo.toml` in the
 `[dev-dependencies]` section. These dependencies are not propagated to other
 packages which depend on this package.
 
-One such example is using a crate that extends standard `assert!` macros.  
+One such example is [`pretty_assertions`](https://docs.rs/pretty_assertions/1.0.0/pretty_assertions/index.html), which extends standard `assert_eq!` and `assert_ne!` macros, to provide colorful diff.  
 File `Cargo.toml`:
 
 ```toml
 # standard crate data is left out
 [dev-dependencies]
-pretty_assertions = "0.4.0"
+pretty_assertions = "1"
 ```
 
 File `src/lib.rs`:
 
 ```rust,ignore
-// externing crate for test-only use
-#[cfg(test)]
-#[macro_use]
-extern crate pretty_assertions;
-
 pub fn add(a: i32, b: i32) -> i32 {
     a + b
 }
 
 #[cfg(test)]
 mod tests {
     use super::*;
+    use pretty_assertions::assert_eq; // crate for test-only use. Cannot be used in non-test code.
 
     #[test]
     fn test_add() {