Prevent release

Summary:
Move the snapshot repository into the SNAPSHOT block.
This will mean that trying to build a release version will now
fail because it can't resolve the dependency like this:

```

FAILURE: Build failed with an exception.

* What went wrong:
Could not determine the dependencies of task ':android:compileReleaseAidl'.
> Could not resolve all task dependencies for configuration ':android:releaseCompileClasspath'.
   > Could not find com.github.facebook:fresco:0ff379c262.
     Searched in the following locations:
       - file:/opt/android-sdk/extras/m2repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.pom
       - file:/opt/android-sdk/extras/m2repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.jar
       - file:/opt/android-sdk/extras/google/m2repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.pom
       - file:/opt/android-sdk/extras/google/m2repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.jar
       - file:/opt/android-sdk/extras/android/m2repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.pom
       - file:/opt/android-sdk/extras/android/m2repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.jar
       - https://dl.google.com/dl/android/maven2/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.pom
       - https://dl.google.com/dl/android/maven2/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.jar
       - file:/home/realpassy/.m2/repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.pom
       - file:/home/realpassy/.m2/repository/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.jar
       - https://repo.maven.apache.org/maven2/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.pom
       - https://repo.maven.apache.org/maven2/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.jar
       - https://jcenter.bintray.com/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.pom
       - https://jcenter.bintray.com/com/github/facebook/fresco/0ff379c262/fresco-0ff379c262.jar
     Required by:
         project :android

* Try:
Run with --stacktrace option to get the stack trace. Run with --info or --debug option to get more log output. Run with --scan to get full insights.

* Get more help at https://help.gradle.org

Deprecated Gradle features were used in this build, making it incompatible with Gradle 6.0.
Use '--warning-mode all' to show the individual deprecation warnings.
See https://docs.gradle.org/5.1.1/userguide/command_line_interface.html#sec:command_line_warnings

BUILD FAILED in 2s
```

Reviewed By: priteshrnandgaonkar

Differential Revision: D14279359

fbshipit-source-id: 6b86a0232d7a4ded8c94bd3a0e0dd08116f13719

build.gradle

@@ -24,11 +24,11 @@ subprojects {
         mavenLocal()
         mavenCentral()
         jcenter()
-        // TODO(T40752310): Remove this once Fresco is stable.
-        maven { url 'https://jitpack.io' }
 
         if (isSnapshot()) {
             maven { url 'https://oss.sonatype.org/content/repositories/snapshots/' }
+            // TODO(T40752310): Remove this once Fresco is stable.
+            maven { url 'https://jitpack.io' }
         }
     }
 }