Bump version to 0.4.1

Author: dashpole

build.gradle

@@ -7,7 +7,7 @@ apply plugin: 'maven'
 apply plugin: "signing"
 
 group = "io.opencensus"
-version = "0.4.1-SNAPSHOT" // CURRENT_OPENCENSUS_PROTO_VERSION
+version = "0.4.1" // CURRENT_OPENCENSUS_PROTO_VERSION
 
 sourceCompatibility = 1.6
 targetCompatibility = 1.6