Fix protobuf version to 3.6.1

(cherry picked from commit 2b8ef61)

Author: rdegnan

.travis.yml

@@ -20,9 +20,12 @@ jobs:
     - LDFLAGS="/usr/local/lib/libprotobuf.a /usr/local/lib/libprotoc.a"
     before_install:
     - brew update
+    - pushd $(brew --repo)/Library/Taps/homebrew/homebrew-core
+    - git checkout 25a1892 Formula/protobuf.rb
     - EDITOR="sed -i '' 's/system \".\/configure\",/system \".\/configure\", \"--disable-shared\",/g'"
       brew edit protobuf
     - brew install protobuf
+    - popd
     script: "./ci/travis.sh"
 before_cache:
 - rm -f $HOME/.gradle/caches/modules-2/modules-2.lock

rsocket-rpc-metrics-idl/build.gradle

@@ -1,13 +1,10 @@
 plugins {
-    id 'com.google.protobuf' version '0.8.6'
+    id 'com.google.protobuf' version '0.8.8'
 }
 
 description = 'RSocket RPC Metrics IDL'
 
 protobuf {
-    protoc {
-        artifact = 'com.google.protobuf:protoc'
-    }
     generateProtoTasks {
         all().each { task ->
             task.enabled = false

rsocket-rpc-protobuf-idl/build.gradle

@@ -1,13 +1,10 @@
 plugins {
-    id 'com.google.protobuf' version '0.8.6'
+    id 'com.google.protobuf' version '0.8.8'
 }
 
 description = 'RSocket RPC Protobf IDL'
 
 protobuf {
-    protoc {
-        artifact = "com.google.protobuf:protoc"
-    }
     generateProtoTasks {
         all().each { task ->
             task.enabled = false