Update spirv-tools to 0.7.0 (#753)

This moves to the v2021.3 version of SPIRV-Tools

Author: Jake-Shadle

Cargo.lock

@@ -44,7 +44,7 @@ sanitize-filename = "0.3"
 serde = { version = "1.0", features = ["derive"] }
 serde_json = "1.0"
 smallvec = "1.6.1"
-spirv-tools = { version = "0.6.1", default-features = false }
+spirv-tools = { version = "0.7", default-features = false }
 topological-sort = "0.1"
 
 [dev-dependencies]