Fix bug in strip_silence thanks to @TuBui

Author: jiaaro

Diff for: pydub/effects.py

@@ -107,7 +107,7 @@ def strip_silence(seg, silence_len=1000, silence_thresh=-16, padding=100):
 
     seg = chunks[0]
     for chunk in chunks[1:]:
-        seg.append(chunk, crossfade=crossfade)
+        seg = seg.append(chunk, crossfade=crossfade)
 
     return seg
 
@@ -338,4 +338,4 @@ def apply_gain_stereo(seg, left_gain=0.0, right_gain=0.0):
 
     return seg._spawn(data=output,
                 overrides={'channels': 2,
-                           'frame_width': 2 * seg.sample_width})
+                           'frame_width': 2 * seg.sample_width})