minor import fix

Author: cwensel

cascading-core/src/test/java/cascading/tuple/InstantTypeTest.java

@@ -23,6 +23,7 @@
 import java.time.Instant;
 
 import cascading.CascadingTestCase;
+import cascading.tuple.coerce.Coercions;
 import cascading.tuple.type.InstantType;
 import org.junit.Test;