Fix build template to match build runner changes

Api changed in 7b57454cc1.

std/special/build_file_template.zig

@@ -1,6 +1,6 @@
 const Builder = @import("std").build.Builder;
 
-pub fn build(b: &Builder) {
+pub fn build(b: &Builder) -> %void {
     const mode = b.standardReleaseOptions();
     const exe = b.addExecutable("YOUR_NAME_HERE", "src/main.zig");
     exe.setBuildMode(mode);