Fix InputTransformer to strip Qt console continuation prompts.

Closes gh-4728

Thanks to the excellent detective work by @y-p, this was an easy fix.

IPython/core/inputtransformer.py

@@ -453,8 +453,7 b' def classic_prompt():'
 def ipy_prompt():
     """Strip IPython's In [1]:/...: prompts."""
     # FIXME: non-capturing version (?:...) usable?
-    # FIXME: r'^(In \[\d+\]: | {3}\.{3,}: )' clearer?
-    prompt_re = re.compile(r'^(In \[\d+\]: |\ \ \ \.\.\.+: )')
+    prompt_re = re.compile(r'^(In \[\d+\]: |\ {3,}\.{3,}: )')
     return _strip_prompts(prompt_re)