Update rand requirement from 0.6.0 to 0.7.0 in /examples

Updates the requirements on [rand](https://github.com/rust-random/rand) to permit the latest version.
- [Release notes](https://github.com/rust-random/rand/releases)
- [Changelog](https://github.com/rust-random/rand/blob/master/CHANGELOG.md)
- [Commits](https://github.com/rust-random/rand/commits)

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

Author: dependabot-preview[bot]

examples/slice_sum/Cargo.toml

@@ -12,4 +12,4 @@ path = "src/main.rs"
 packed_simd = { path = "../.." }
 rayon = "^1.0"
 time = "^0.1"
-rand = "0.6.0"
+rand = "0.7.0"

examples/triangle_xform/Cargo.toml

@@ -8,5 +8,5 @@ edition = "2018"
 packed_simd = { path = "../.." }
 
 [dev-dependencies]
-rand = "0.6.0"
+rand = "0.7.0"
 time = "0.1.40"