Tweak box drawing

So it doesn't hit weird positron highlighting buglet

Author: hadley

R/parallel.R

@@ -1,4 +1,4 @@
-# +-----------------------------+     +-------------------------------+
+# /-----------------------------\     /-------------------------------\
 # | Main R process              |     | Subprocess 1                  |
 # | +------------------------+  |     | +---------------------------+ |
 # | | test_dir_parallel()    |  |     | | test_file()               | |
@@ -11,17 +11,16 @@
 # | | | Progress2Reporter |  |  |  |  | | |    v                  | | |
 # | | +-------------------+  |  |  |  | | | +-------------------+ | | |
 # | +------------------------+  |  |--------| signalCondition() | | | |
-# +-----------------------------+  |  | | | +-------------------+ | | |
+# \-----------------------------/  |  | | | +-------------------+ | | |
 #                                  |  | | +-----------------------+ | |
 #                                  |  | +---------------------------+ |
-#                                  |  +-------------------------------+
-#                                  |  +-------------------------------+
+#                                  |  \-------------------------------/
+#                                  |  /-------------------------------\
 #                                  |--| Subprocess 2                  |
-#                                  |  +-------------------------------+
-#                                  |  +-------------------------------+
-#                                  +--| Subprocess 3                  |
-#                                     +-------------------------------+
-#                                       ...
+#                                  |  \-------------------------------/
+#                                  |  /-------------------------------\
+#                                  \--| Subprocess 3                  |
+#                                     \-------------------------------/
 #
 # ## Notes
 #