Fix typo

"the system bring flashed" -> "the system being flashed"

The letters are right next to one another. Really.

Change-Id: I7d224d280e1fe0c77bf0574f327afb977e58e2a0
diff --git a/src/source/building-devices.md b/src/source/building-devices.md
index f298e5a..8b1dae7 100644
--- a/src/source/building-devices.md
+++ b/src/source/building-devices.md
@@ -135,7 +135,7 @@
 
 An entire Android system can be flashed in a single command: this writes
 the boot, recovery and system partitions together after verifying that the
-system bring flashed is compatible with the installed bootloader and radio,
+system being flashed is compatible with the installed bootloader and radio,
 and reboots the system.
 
     $ fastboot flashall