upip: Fix heap size to use for decreased gzip dictionary.

Original intended value is 64K of heap or smaller, 640K figure was a
testing one.

upip/upip.py

@@ -170,7 +170,7 @@ def install(to_install, install_path=None):
     # Calculate gzip dictionary size to use
     global gzdict_sz
     sz = gc.mem_free() + gc.mem_alloc()
-    if sz <= 655360:
+    if sz <= 65536:
         gzdict_sz = 16 + 12
 
     if install_path is None: