fix plot_dataframe.py lint warnings

scripts/plot_dataframe.py

@@ -1,11 +1,11 @@
 #!/usr/bin/env python3
 
 import matplotlib  # Install PYQT5 manually if you want to test this helper function
-matplotlib.use("Qt5Agg")
 import matplotlib.pyplot as plt
-
 from freqtrade import exchange, analyze
 
+matplotlib.use("Qt5Agg")
+
 
 def plot_analyzed_dataframe(pair: str) -> None:
     """
@@ -52,4 +52,3 @@ def plot_analyzed_dataframe(pair: str) -> None:
 
 if __name__ == '__main__':
     plot_analyzed_dataframe('BTC_ETH')
-