[BREAKING CHANGE] change variable keyword to 'let' from 'var'

scripts/array.rhai

@@ -1,4 +1,4 @@
-var x = [1, 2, 3];
+let x = [1, 2, 3];
 print(x[1]);
 x[1] = 5;
 print(x[1]);

scripts/assignment.rhai

@@ -1,2 +1,2 @@
-var x = 78
+let x = 78
 print(x)

scripts/if1.rhai

@@ -1,5 +1,5 @@
-var a = true;
+let a = true;
 if (a) {
-    var x = 56;
+    let x = 56;
     print(x);
 }

scripts/speed_test.rhai

@@ -1,4 +1,4 @@
-var x = 1000000;
+let x = 1000000;
 while x > 0 {
     x = x - 1;
 }

scripts/while.rhai

@@ -1,4 +1,4 @@
-var x = 10;
+let x = 10;
 
 while x > 0 {
     print(x);