Update structopt requirement from ^0.2 to ^0.3 in /examples

Updates the requirements on [structopt](https://github.com/TeXitoi/structopt) to permit the latest version.
- [Release notes](https://github.com/TeXitoi/structopt/releases)
- [Changelog](https://github.com/TeXitoi/structopt/blob/master/CHANGELOG.md)
- [Commits](TeXitoi/structopt@v0.2.10...v0.3.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

examples/aobench/Cargo.toml

@@ -14,7 +14,7 @@ name = "aobench_lib"
 path = "src/lib.rs"
 
 [dependencies]
-structopt = "^0.2"
+structopt = "^0.3"
 failure = "^0.1"
 png = "^0.15"
 packed_simd = { path = "../.." }

examples/mandelbrot/Cargo.toml

@@ -9,7 +9,7 @@ edition = "2018"
 packed_simd = { path = "../.." }
 rayon = "^1.0"
 ispc = { version = "^1.0.4", optional = true }
-structopt = "0.2.10"
+structopt = "0.3.0"
 
 [build-dependencies]
 ispc = { version = "^1.0.4", optional = true }