adjusted stretch code

Author: bscott519

lesson_06/benjaminscott/README.md

@@ -2,7 +2,7 @@
 
 ```
 function isValidAlphaAbbreviation(word: string, abbr: string): boolean {
-    var letterToNum = { "a": 1, "b": 2, "c": 3, "d": 4, "e": 5, "f": 6, "g": 7, "h": 8, "i": 9, "j": 10, "k": 11, "l": 12, "m": 13, "n": 14, "o": 15, "p": 16, "q": 17, "r": 18, "s": 19, "t": 20, "u": 21, "v": 22, "w": 23, "x": 24, "y": 25, "z": 26 };
+    const letterToNum = { "a": 1, "b": 2, "c": 3, "d": 4, "e": 5, "f": 6, "g": 7, "h": 8, "i": 9, "j": 10, "k": 11, "l": 12, "m": 13, "n": 14, "o": 15, "p": 16, "q": 17, "r": 18, "s": 19, "t": 20, "u": 21, "v": 22, "w": 23, "x": 24, "y": 25, "z": 26 };
     let wordIndex = 0;
     let abbrIndex = 0;