escape quotes in string in description field (#76)

diff --git a/.asf.yaml b/.asf.yaml
index 9cabea1..2316637 100644
--- a/.asf.yaml
+++ b/.asf.yaml
@@ -16,7 +16,7 @@
 #
 
 github:
-  description: "Apache OpenWhisk SDK for building Docker "blackbox" runtimes"
+  description: "Apache OpenWhisk SDK for building Docker \"blackbox\" runtimes"
   homepage: https://openwhisk.apache.org/
   labels:
   - openwhisk