Merge pull request swagger-api#1175 from swagger-api/update-slf4j

update pom slf4j in v3

Author: gracekarina

pom.xml

@@ -287,7 +287,7 @@
     <properties>
         <swagger-parser-v2-version>1.0.46-SNAPSHOT</swagger-parser-v2-version>
         <commons-io-version>2.4</commons-io-version>
-        <slf4j-version>1.6.3</slf4j-version>
+        <slf4j-version>1.7.28</slf4j-version>
         <swagger-core-version>2.0.9-SNAPSHOT</swagger-core-version>
         <junit-version>4.8.1</junit-version>
         <testng-version>6.14.2</testng-version>