Fixed calling not defined pi in phase

proxtoolbox/Problems/Phase/phase.py

@@ -33,7 +33,7 @@ class Phase(Problem):
         #moved here from JWST_in since if statements not possible in dictonary
         if 'distance' in self.config:
             if self.config['distance'] =='near field':
-                self.config['fresnel_nr'] = 1*2*pi*self.config['Nx']
+                self.config['fresnel_nr'] = 1*2*np.pi*self.config['Nx']
                 self.config['use_farfield_formula'] = 0
             else:
                 self.config['fresnel_nr'] = 0