Pin perf dependency on firebase-datatransport (#5056)

Author: rlazo

firebase-perf/firebase-perf.gradle

@@ -102,7 +102,7 @@ dependencies {
     implementation "com.google.protobuf:protobuf-javalite:$javaliteVersion"
     runtimeOnly 'com.google.firebase:firebase-installations:17.1.3'
     implementation 'com.google.android.datatransport:transport-api:3.0.0'
-    runtimeOnly project(':firebase-datatransport')
+    runtimeOnly 'com.google.firebase:firebase-datatransport:18.1.8'
     javadocClasspath 'com.google.auto.value:auto-value-annotations:1.6.6'
     javadocClasspath 'com.google.code.findbugs:jsr305:3.0.2'