typo fix

code/band_structures.py

@@ -145,10 +145,10 @@ def main():
     phonons_1d_2masses()
     meff_1d_tb()
     tight_binding_1d()
-    DOS_finite_phonon_chain(3, 3_phonons.svg)
-    DOS_finite_phonon_chain(300, 300_phonons.svg)
-    DOS_finite_electron_chain(3, 3_electrons.svg)
-    DOS_finite_electron_chain(300, 300_electrons.svg)
+    DOS_finite_phonon_chain(3, '3_phonons.svg')
+    DOS_finite_phonon_chain(300, '300_phonons.svg')
+    DOS_finite_electron_chain(3, '3_electrons.svg')
+    DOS_finite_electron_chain(300, '300_electrons.svg')
 
 if __name__ == "__main__":
     main()