mutable decl syntax change

examples/programs/inline/main.bro

@@ -68,8 +68,8 @@ main func() i32 {
 		return 2
 	}
 
-	a Value = .number{41}
-	b Value = .number{41}
+	a Value := .number{41}
+	b Value := .number{41}
 	if !equal_value(a, b) or equal_value(a, .pair{left = 41, right = 0}) {
 		return 3
 	}
@@ -78,8 +78,8 @@ main func() i32 {
 		return 4
 	}
 
-	pair_a Value = .pair{left = 2, right = 3}
-	pair_b Value = .pair{left = 2, right = 3}
+	pair_a Value := .pair{left = 2, right = 3}
+	pair_b Value := .pair{left = 2, right = 3}
 	if !equal_value(pair_a, pair_b) or !equal_value(.empty, .empty) {
 		return 5
 	}
@@ -88,7 +88,7 @@ main func() i32 {
 		return 6
 	}
 
-	empty Value = .empty
+	empty Value := .empty
 	increment(&empty)
 	return 0
 }