created a new exercise about vectors in zig, gave it number 109

build.zig

@@ -1201,6 +1201,13 @@ const exercises = [_]Exercise{
         .main_file = "108_labeled_switch.zig",
         .output = "The pull request has been merged.",
     },
+    .{
+        .main_file = "109_vectors.zig",
+        .output =
+        \\Max difference (old fn): 0.014
+        \\Max difference (new fn): 0.014
+        ,
+    },
     .{
         .main_file = "999_the_end.zig",
         .output =