Make LexeMatcher package-private.

We don't need it outside of the `formula` package.

This fixes warnings about exposing Lexeme outside of its visibility
scope, so yay.

src/test/java/com/garbagemule/MobArena/formula/LexemeMatcher.java

@@ -6,7 +6,7 @@ import org.hamcrest.TypeSafeMatcher;
 
 import java.util.Objects;
 
-public class LexemeMatcher extends TypeSafeMatcher<Lexeme> {
+class LexemeMatcher extends TypeSafeMatcher<Lexeme> {
 
     private final TokenType type;
     private final String value;