ci: fix .travis.yml syntax for conditional deployments

Was scilently missing `on:` section :(

https://docs.travis-ci.com/user/deployment/#conditional-releases-with-on

Signed-off-by: Alexander Bezzubov <bzz@apache.org>

.travis.yml

@@ -68,7 +68,8 @@ jobs:
         file_glob: true
         file: build/*.tar.gz
         skip_cleanup: true
-        tags: true
+        on:
+          tags: true
 
     - name: 'linux shared lib'
       stage: release
@@ -82,7 +83,8 @@ jobs:
         file:
           - ./.shared/linux-x86-64/libenry.so
         skip_cleanup: true
-        tags: true
+        on:
+          tags: true
 
     - name: 'macOS shared lib'
       stage: release
@@ -105,7 +107,8 @@ jobs:
           secure: $GITHUB_TOKEN
         file: ./.shared/darwin/libenry.dylib
         skip_cleanup: true
-        tags: true
+        on:
+          tags: true
 
     - name: 'java: publish to maven'
       stage: publish
@@ -140,4 +143,5 @@ jobs:
         file_glob: true
         file: ./target/enry-java*.jar
         skip_cleanup: true
-        tags: true
+        on:
+          tags: true