Update key for 1.15.1 to use full fingerprint (#123)

diff --git a/1.15/scala_2.12-java11-debian/Dockerfile b/1.15/scala_2.12-java11-debian/Dockerfile
index 00d9811..1ba473e 100644
--- a/1.15/scala_2.12-java11-debian/Dockerfile
+++ b/1.15/scala_2.12-java11-debian/Dockerfile
@@ -46,7 +46,7 @@
 # Configure Flink version
 ENV FLINK_TGZ_URL=https://www.apache.org/dyn/closer.cgi?action=download&filename=flink/flink-1.15.1/flink-1.15.1-bin-scala_2.12.tgz \
     FLINK_ASC_URL=https://www.apache.org/dist/flink/flink-1.15.1/flink-1.15.1-bin-scala_2.12.tgz.asc \
-    GPG_KEY=3EE012FEE982F098 \
+    GPG_KEY=7D660377995CA7A5AFEBA79A3EE012FEE982F098 \
     CHECK_GPG=true
 
 # Prepare environment
diff --git a/1.15/scala_2.12-java8-debian/Dockerfile b/1.15/scala_2.12-java8-debian/Dockerfile
index ed38e2a..5fcb32c 100644
--- a/1.15/scala_2.12-java8-debian/Dockerfile
+++ b/1.15/scala_2.12-java8-debian/Dockerfile
@@ -46,7 +46,7 @@
 # Configure Flink version
 ENV FLINK_TGZ_URL=https://www.apache.org/dyn/closer.cgi?action=download&filename=flink/flink-1.15.1/flink-1.15.1-bin-scala_2.12.tgz \
     FLINK_ASC_URL=https://www.apache.org/dist/flink/flink-1.15.1/flink-1.15.1-bin-scala_2.12.tgz.asc \
-    GPG_KEY=3EE012FEE982F098 \
+    GPG_KEY=7D660377995CA7A5AFEBA79A3EE012FEE982F098 \
     CHECK_GPG=true
 
 # Prepare environment