vbox: fix typo

Change-Id: Ie6de3bb2385a9da4c1753a3b1c8473bfa09f4856
diff --git a/vbox/env.sh b/vbox/env.sh
index 8f65ade..eeb1347 100755
--- a/vbox/env.sh
+++ b/vbox/env.sh
@@ -25,7 +25,7 @@
 export FUCHSIA_VBOX_CPUS
 export FUCHSIA_VBOX_RAM=${FUCHSIA_VBOX_RAM:-4096}
 export FUCHSIA_VBOX_VRAM=${FUCHSIA_VBOX_VRAM:-128}
-export FUCHSIA_VBOX_DISK_SIZE=${FUCHSIA_VBOX_DISK_SIZE:-4g)}
+export FUCHSIA_VBOX_DISK_SIZE=${FUCHSIA_VBOX_DISK_SIZE:-4g}
 export FUCHSIA_VBOX_RAW=${FUCHSIA_VBOX_RAW:-$FUCHSIA_OUT_DIR/vbox/disk.raw}
 export FUCHSIA_VBOX_VMDK=${FUCHSIA_VBOX_VMDK:-$FUCHSIA_OUT_DIR/vbox/disk.vmdk}
 export FUCHSIA_VBOX_CONSOLE_SOCK=${FUCHSIA_VBOX_CONSOLE_SOCK:-"$FUCHSIA_OUT_DIR/vbox/${FUCHSIA_VBOX_NAME}.sock"}