Fix grammar in comment

Author: shewitt-au

lib/include/pl/core/lexer.hpp

@@ -21,7 +21,7 @@ namespace pl::core {
 
         hlp::CompileResult<std::vector<Token>> lex(const api::Source *source);
         size_t getLongestLineLength() const { 
-            // 'getLongestLineLength' is used my the pattern editor to control
+            // 'getLongestLineLength' is used by the pattern editor to control
             // the x-scrolling range. Adding two makes the whole longest line visible.
             // Not sure why we have to do this.
             return m_longestLineLength+2;