generator: Upgrade vk-parse to 0.15 for <feature> inside interface items

Includes changes from krolli/vk-parse#33.
Fixes #937.

Author: MarijnS95

generator/Cargo.toml

@@ -17,7 +17,7 @@ once_cell = "1.7"
 proc-macro2 = "1.0"
 quote = "1.0"
 regex = "1.4"
-vk-parse = { version = "0.14", features = ["vkxml-convert"] }
+vk-parse = { version = "0.15", features = ["vkxml-convert"] }
 vkxml = "0.3"
 
 [dependencies.syn]