Change convplot output name to haev case name in it

.gitignore

@@ -37,4 +37,4 @@
 *.ip
 
 # ignore convergence plots
-*convergence_plot.pdf
\ No newline at end of file
+*convergence_plot*.pdf
\ No newline at end of file

src/postprocessor.py

@@ -27,7 +27,7 @@ class Postprocessor:
             import matplotlib.pyplot as plt # pylint: disable=C0413
         """
 
-        filename = "convergence_plot.pdf"
+        filename = "convergence_plot_" + self.output_folder  + ".pdf"
 
         plt.figure(num=None, figsize=(16, 9), dpi=100)