Apply more let/const transforms.

_baseSortedIndexBy.js

@@ -1,12 +1,11 @@
 import isSymbol from './isSymbol.js';
 
 /** Used as references for the maximum length and index of an array. */
-var MAX_ARRAY_LENGTH = 4294967295,
-    MAX_ARRAY_INDEX = MAX_ARRAY_LENGTH - 1;
+const MAX_ARRAY_LENGTH = 4294967295;
+const MAX_ARRAY_INDEX = MAX_ARRAY_LENGTH - 1;
 
 /* Built-in method references for those with the same name as other `lodash` methods. */
-var nativeFloor = Math.floor,
-    nativeMin = Math.min;
+const nativeFloor = Math.floor, nativeMin = Math.min;
 
 /**
  * The base implementation of `_.sortedIndexBy` and `_.sortedLastIndexBy`
@@ -24,20 +23,20 @@ var nativeFloor = Math.floor,
 function baseSortedIndexBy(array, value, iteratee, retHighest) {
   value = iteratee(value);
 
-  var low = 0,
-      high = array == null ? 0 : array.length,
-      valIsNaN = value !== value,
-      valIsNull = value === null,
-      valIsSymbol = isSymbol(value),
-      valIsUndefined = value === undefined;
+  let low = 0;
+  let high = array == null ? 0 : array.length;
+  const valIsNaN = value !== value;
+  const valIsNull = value === null;
+  const valIsSymbol = isSymbol(value);
+  const valIsUndefined = value === undefined;
 
   while (low < high) {
-    var mid = nativeFloor((low + high) / 2),
-        computed = iteratee(array[mid]),
-        othIsDefined = computed !== undefined,
-        othIsNull = computed === null,
-        othIsReflexive = computed === computed,
-        othIsSymbol = isSymbol(computed);
+    const mid = nativeFloor((low + high) / 2);
+    const computed = iteratee(array[mid]);
+    const othIsDefined = computed !== undefined;
+    const othIsNull = computed === null;
+    const othIsReflexive = computed === computed;
+    const othIsSymbol = isSymbol(computed);
 
     if (valIsNaN) {
       var setLow = retHighest || othIsReflexive;