Change default optimizations pass to focus on code size (#305)

* Change default opitmization pass to focus on code size

* Change default optimization level from `-Os` to `-Oz`

* Update CHANGELOG

Author: HCastano

CHANGELOG.md

@@ -6,6 +6,9 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 
 ## [Unreleased]
 
+### Changed
+- Change default optimizations pass to focus on code size - [#305](https://github.com/paritytech/cargo-contract/pull/305)
+
 ## [0.12.1] - 2021-04-25
 
 ### Added

src/cmd/build.rs

@@ -81,7 +81,7 @@ pub struct BuildCommand {
     ///
     /// - `z`, execute default optimization passes, super-focusing on code size
     ///
-    /// - The default value is `3`
+    /// - The default value is `z`
     ///
     /// - It is possible to define the number of optimization passes in the
     ///   `[package.metadata.contract]` of your `Cargo.toml` as e.g. `optimization-passes = "3"`.

src/main.rs

@@ -128,7 +128,7 @@ impl Display for OptimizationPasses {
 
 impl Default for OptimizationPasses {
     fn default() -> OptimizationPasses {
-        OptimizationPasses::Three
+        OptimizationPasses::Z
     }
 }