Add missing period in some rule messages (#266)

Author: JLHwung

rules/no-nested-tests.js

@@ -16,7 +16,7 @@ const create = context => {
 			if (nestedCount >= 2) {
 				context.report({
 					node,
-					message: 'Tests should not be nested'
+					message: 'Tests should not be nested.'
 				});
 			}
 		}),

rules/test-title-format.js

@@ -27,7 +27,7 @@ const create = context => {
 				if (title.type === 'Literal' && !titleRegExp.test(title.value)) {
 					context.report({
 						node,
-						message: `The test title doesn't match the required format: \`${titleRegExp}\``
+						message: `The test title doesn't match the required format: \`${titleRegExp}\`.`
 					});
 				}
 			}

test/no-nested-tests.js

@@ -11,7 +11,7 @@ const ruleTester = avaRuleTester(test, {
 const header = 'const test = require(\'ava\');\n';
 const error = {
 	ruleId: 'no-nested-tests',
-	message: 'Tests should not be nested'
+	message: 'Tests should not be nested.'
 };
 
 ruleTester.run('no-nested-tests', rule, {