Quote consistency.

Author: objcode

coroutines-codelab/build.gradle

@@ -27,7 +27,7 @@ buildscript {
         def appcompat_version = '1.1.0'
         def constraint_layout_version = '1.1.3'
         def coroutines_android_version = '1.2.1'
-        def expresso_version = "3.1.1"
+        def expresso_version = '3.1.1'
         def junit_version = '4.12'
         def lifecycle_version = '2.1.0'
         def material_version = '1.2.0-alpha01'