Update pekko_version to 1.4.0 (#22)

Author: pjfanning

src/main/g8/default.properties

@@ -1,6 +1,6 @@
 name=My Pekko HTTP Project
 pekko_http_version=1.3.0
-pekko_version=1.2.1
+pekko_version=1.4.0
 organization=com.example
 package=$organization$
-verbatim=gradlew gradlew.bat gradle-wrapper.properties gradle-wrapper.jar
+verbatim=gradlew gradlew.bat gradle-wrapper.properties gradle-wrapper.jar