Incorrect file endings in .pvd file

[DavidVonRueden]

Hello,
First of all, thank you for this tool!
I ran into an issue using the conversion from .frd to vtu. The conversion to to .vtu works just fine resulting in files like:
shell.01.vtu
shell.02.vtu
....
The created .pvd file then contains

		<DataSet file="shell.01vtu" timestep="0.002"/>
		<DataSet file="shell.02vtu" timestep="0.004"/>

Due to the missing dot, the correct .vtu files can't be opened.
I could resolve this issue by changing the following section:

ccx2paraview/ccx2paraview.py

Lines 959 to 963 in 43287b5

	for step, inc, num in self.step_inc_num():
	file_name = os.path.basename(self.frd_file_name[:-4]) + num
	f.write('\t\t<DataSet file="{}vtu" timestep="{}"/>\n'\
	.format(os.path.basename(file_name), inc))

f.write('\t\t<DataSet file="{}.vtu" timestep="{}"/>\n'\ 
         .format(os.path.basename(file_name), inc))

Can you confirm this behaviour on your side?