Fix <- in markdown (#1159)

Author: tirkarthi

docs/fsharp/language-reference/values/index.md

@@ -35,7 +35,7 @@ F# is not a pure functional language, yet it fully supports functional programmi
 ## Mutable Variables
 You can use the keyword `mutable` to specify a variable that can be changed. Mutable variables in F# should generally have a limited scope, either as a field of a type or as a local value. Mutable variables with a limited scope are easier to control and are less likely to be modified in incorrect ways.
 
-You can assign an initial value to a mutable variable by using the `let` keyword in the same way as you would define a value. However, the difference is that you can subsequently assign new values to mutable variables by using the `<-` operator, as in the following example.
+You can assign an initial value to a mutable variable by using the `let` keyword in the same way as you would define a value. However, the difference is that you can subsequently assign new values to mutable variables by using the `<-` operator, as in the following example.
 
 [!code-fsharp[Main](../../../../samples/snippets/fsharp/lang-ref-1/snippet602.fs)]
 
@@ -50,4 +50,4 @@ You can assign an initial value to a mutable variable by using the `let` keyword
 ## See Also
 [Null Values](null-Values.md)
 
-[F# Language Reference](../index.md)
+[F# Language Reference](../index.md)