Herp derp. It's actually constant-time append.

Change-Id: I16dfbdec88c14a12214fbe2efcea3f693bfdfc11
Reviewed-on: https://code-review.googlesource.com/c/re2/+/57390
Reviewed-by: Paul Wankadia <junyer@google.com>
diff --git a/re2/compile.cc b/re2/compile.cc
index 4ba2852..7a9de07 100644
--- a/re2/compile.cc
+++ b/re2/compile.cc
@@ -70,7 +70,7 @@
   }
 
   uint32_t head;
-  uint32_t tail;  // for linear-time append
+  uint32_t tail;  // for constant-time append
 };
 
 static const PatchList kNullPatchList = {0, 0};