More spelling changes.

src/platform-cygwin.cc

Index: src/platform-cygwin.cc
===================================================================
--- src/platform-cygwin.cc	(revision 10402)
+++ src/platform-cygwin.cc	(working copy)
@@ -114,7 +114,7 @@
 
 // We keep the lowest and highest addresses mapped as a quick way of
 // determining that pointers are outside the heap (used mostly in assertions
-// and verification).  The estimate is conservative, ie, not all addresses in
+// and verification).  The estimate is conservative, i.e., not all addresses in
 // 'allocated' space are actually allocated to our heap.  The range is
 // [lowest, highest), inclusive on the low and and exclusive on the high end.
 static void* lowest_ever_allocated = reinterpret_cast<void*>(-1);