drop golang1.13 and golang1.15 (#167)

Author: dgrove-oss

.travis.yml

@@ -51,7 +51,7 @@ deploy:
       repo: apache/openwhisk-runtime-go
   - provider: script
     skip_cleanup: true
-    script: "./tools/travis/publish.sh openwhisk 1.13 nightly && ./tools/travis/publish.sh openwhisk 1.15 nightly && ./tools/travis/publish.sh openwhisk 1.16 nightly && ./tools/travis/publish.sh openwhisk 1.17 nightly && ./tools/travis/publish.sh openwhisk 1.18 nightly"
+    script: "./tools/travis/publish.sh openwhisk 1.16 nightly && ./tools/travis/publish.sh openwhisk 1.17 nightly && ./tools/travis/publish.sh openwhisk 1.18 nightly"
     on:
       branch: master
       repo: apache/openwhisk-runtime-go

docs/BUILD.md

@@ -43,9 +43,9 @@ To build the docker images, after compiling go proxy:
 
 This will build the images:
 
-* `action-golang-v1.13`: an image supporting Go 1.13 sources (does expect an ack)
-* `action-golang-v1.15`: an image supporting Go 1.15 sources (does expect an ack)
 * `action-golang-v1.16`: an image supporting Go 1.16 sources (does expect an ack)
+* `action-golang-v1.17`: an image supporting Go 1.17 sources (does expect an ack)
+* `action-golang-v1.18`: an image supporting Go 1.18 sources (does expect an ack)
 * `actionloop-base`: the base image, supporting generic executables ans shell script (does not expect an ack)
 
 The `actionloop-base` image can be used for supporting other compiled programming languages as long as they implement a `compile` script and the *action loop* protocol described below. Please check [ENVVARS.md](ENVVARS.md) for configuration options

docs/DEPLOY.md

@@ -19,7 +19,7 @@
 
 # Deployment options
 
-There are a few images provided: the `actionloop-base` and the `action-golang-v1.13`, `action-golang-v1.15` and `action-golang-v1.16` are available. Each image accepts different input in the deployment.
+There are a few images provided: the `actionloop-base` and the `action-golang-v1.16`, `action-golang-v1.17` and `action-golang-v1.18` are available. Each image accepts different input in the deployment.
 
 <a name="actionloop">