Fix: custom_stoploss returns typo

Afaik it should return -0.07 for 7% instead of -0.7.

As a side note, really interesting would also be an example for greater than 100% profits. especially when trailing stoploss, like
* Once profit is > 200% - stoploss will be set to 150%.

I assume it could be as simple as
```py
if current_profit > 2:
            return (-1.50 + current_profit)
````
to achieve it

But I'm not quite confident, if the bot can handle stuff smaller than `-1`, since `1` and `-1` seem to have some special meaning and are often used to disable stoploss etc.

docs/strategy-advanced.md

@@ -176,7 +176,7 @@ class AwesomeStrategy(IStrategy):
         if current_profit > 0.25:
             return (-0.15 + current_profit)
         if current_profit > 0.20:
-            return (-0.7 + current_profit)
+            return (-0.07 + current_profit)
         return 1
 ```