Fix inline example with missing getter method

Author: biboudis

docs/docs/reference/metaprogramming/inline.md

@@ -79,19 +79,20 @@ In the `true` case the code will be rewritten to:
 def factorial(n: BigInt): BigInt = {
   val msg = s"factorial($n)"
   println(s"${"  " * indent}start $msg")
-  Logger.inline$indent += indentSetting
+  Logger.inline$indent_=(indent.+(indentSetting))
   val result =
     if (n == 0) 1
     else n * factorial(n - 1)
-  Logger.inline$indent -= indentSetting
+  Logger.inline$indent_=(indent.-(indentSetting))
   println(s"${"  " * indent}$msg = $result")
   result
 }
 ```
 
 Note, that the by-value parameter is evaluated only once, per the usual Scala
 semantics, by binding the value and reusing the `msg` through the body of
-`factorial`.
+`factorial`. Also, note the special handling of setting to the private var
+`indent` by generating the setter method `def inline$indent_=`.
 
 ### Recursive Inline Methods