Fix documentation references to tests folder

docs/developer.md

@@ -30,7 +30,7 @@ These are available from `conftest.py` and can be imported in any test module.
 A sample check looks as follows:
 
 ``` python
-from freqtrade.tests.conftest import log_has, log_has_re
+from tests.conftest import log_has, log_has_re
 
 def test_method_to_test(caplog):
     method_to_test()

docs/plotting.md

@@ -179,5 +179,5 @@ freqtrade plot-profit  -p LTC/BTC --db-url sqlite:///tradesv3.sqlite --trade-sou
 ```
 
 ``` bash
-freqtrade plot-profit --datadir ../freqtrade/freqtrade/tests/testdata-20171221/ -p LTC/BTC
+freqtrade plot-profit --datadir user_data/data/binance_save/ -p LTC/BTC
 ```