Fix process-graph.py after #698787, take 2

After the Python 3 conversion, there is now an extra space in the output. This
shows the problem:

>>> print "a\n", "b"
a
b
>>> from __future__ import print_function
>>> print("a\n", "b")
a
 b

Fix it by specifying sep="".

TBR=thakis

Bug: 1007195
Change-Id: I20fea51951d552fcffee4704bd515c54bb84ef63
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1821598Reviewed-by: Hans Wennborg <hans@chromium.org>
Cr-Commit-Position: refs/heads/master@{#699286}

tools/clang/blink_gc_plugin/process-graph.py

@@ -313,7 +313,7 @@ def report_cycle(root_edge):
   sout = out.getvalue()
   if not is_ignored_cycle(sout):
     print("\nFound a potentially leaking cycle starting from a GC root:\n",
-          sout)
+          sout, sep="")
     set_reported_error(True)
 
 def load_graph():