[magma] typo

Test: CQ

Change-Id: I5ca734b1f2febb698d28dd903a1aacacd1d76c36
diff --git a/lib/magma/docs/contributing.md b/lib/magma/docs/contributing.md
index 636e326..5118d55 100644
--- a/lib/magma/docs/contributing.md
+++ b/lib/magma/docs/contributing.md
@@ -43,7 +43,7 @@
 
 Includes all unit tests and integration tests.  There are 2 steps at this tps level:
 
-1. Build with --arg magma_enable_developer_mode=true; this will run unit tests that require hardware,
+1. Build with --args magma_enable_developer_mode=true; this will run unit tests that require hardware,
 then present the device as usual for general applications.  Inspect the syslog for test results.
 
 2. Run the test script [lib/magma/scripts/test.sh](../../../lib/magma/scripts/test.sh) and inspect the test results.