SkQP: fix a typo in script

No-Try: true
Change-Id: I584d21220a0d7bf624373d0eb4a9eeb83ef23d00
Reviewed-on: https://skia-review.googlesource.com/c/174311
Reviewed-by: Hal Canary <halcanary@google.com>
Commit-Queue: Hal Canary <halcanary@google.com>

tools/skqp/docker_build_universal_apk.sh

@@ -14,7 +14,7 @@ cd "${SKIA_ROOT}/infra/skqp/docker"
 docker build -t android-skqp ./android-skqp/
 docker run --rm --privileged -d --name android_em \
         --env=DEVICE="Samsung Galaxy S6" \
-        ---volume="$SKIA_ROOT":/SRC \
+        --volume="$SKIA_ROOT":/SRC \
         --volume="$OUT":/OUT \
         --volume="$BUILD":/BUILD \
         android-skqp