all: Use the name MicroPython consistently in comments

There were several different spellings of MicroPython present in comments,
when there should be only one.
diff --git a/py/objset.c b/py/objset.c
index f74bc74..376439b 100644
--- a/py/objset.c
+++ b/py/objset.c
@@ -1,5 +1,5 @@
 /*
- * This file is part of the Micro Python project, http://micropython.org/
+ * This file is part of the MicroPython project, http://micropython.org/
  *
  * The MIT License (MIT)
  *