Fix base of pow and sub being nonencased

Cargo.toml

@@ -2,7 +2,7 @@
 name = "asciimath-rs"
 description = "AsciiMath parser"
 repository = "https://github.com/trivernis/asciimath-rs"
-version = "0.5.5"
+version = "0.5.6"
 authors = ["trivernis <trivernis@protonmail.com>"]
 edition = "2018"
 readme = "README.md"

src/parsing/tree_parser.rs

@@ -431,7 +431,7 @@ impl TreeParser {
             self.step();
             self.step();
             Some(Pow {
-                base: previous.to_non_enclosed().boxed(),
+                base: previous.clone().boxed(),
                 exp: self.parse_element().unwrap().to_non_enclosed().boxed(),
             })
         } else {
@@ -445,7 +445,7 @@ impl TreeParser {
             self.step();
             self.step();
             Some(Sub {
-                base: previous.to_non_enclosed().boxed(),
+                base: previous.clone().boxed(),
                 lower: self.parse_element().unwrap().to_non_enclosed().boxed(),
             })
         } else {