Fix Typo in Flow Validation

Author: frankfiorante

spring-integration-core/src/main/java/org/springframework/integration/dsl/IntegrationFlowDefinition.java

@@ -3143,7 +3143,7 @@ protected StandardIntegrationFlow get() {
 				}
 				else if (this.currentMessageChannel != null) {
 					throw new BeanCreationException("The 'IntegrationFlow' can't consist of only one 'MessageChannel'. "
-							+ "Add at lest '.bridge()' EIP-method before the end of flow.");
+							+ "Add at least '.bridge()' EIP-method before the end of flow.");
 				}
 			}