Add find msbuild vs16 logic.

src/windows_registry.rs

@@ -727,7 +727,9 @@ mod impl_ {
     // see http://stackoverflow.com/questions/328017/path-to-msbuild
     pub fn find_msbuild(target: &str) -> Option<Tool> {
         // VS 15 (2017) changed how to locate msbuild
-        if let Some(r) = find_msbuild_vs15(target) {
+        if let Some(r) = find_msbuild_vs16(target) {
+            return Some(r);
+        } else if let Some(r) = find_msbuild_vs15(target) {
             return Some(r);
         } else {
             find_old_msbuild(target)