build.gradle: Avoid assignment to japicmp configuration
Instead of assignment, it now seems to be a FileCollection that you
modify. This has probably been broken since f458f22.
```
> Could not create task ':grpc-auth:japicmp'.
> Cannot set the value of read-only property 'oldClasspath' for task ':grpc-auth:japicmp' of type me.champeau.gradle.japicmp.JapicmpTask.
```
The change works with or without the files(), but the conversion is just
not needed anymore as it is handled by FileCollection.
diff --git a/build.gradle b/build.gradle
index 0d76097..aad5a54 100644
--- a/build.gradle
+++ b/build.gradle
@@ -433,8 +433,8 @@
// Add a japicmp task that compares the current .jar with baseline .jar
tasks.register("japicmp", me.champeau.gradle.japicmp.JapicmpTask) {
dependsOn jar
- oldClasspath = files(baselineArtifact)
- newClasspath = files(jar.archiveFile)
+ oldClasspath.from baselineArtifact
+ newClasspath.from jar.archiveFile
onlyBinaryIncompatibleModified = false
// Be quiet about things that did not change
onlyModified = true
