Use okhttp's Credentials class to build basic auth string

modules/swagger-codegen/src/main/resources/Java/libraries/okhttp-gson/auth/HttpBasicAuth.mustache

@@ -2,7 +2,7 @@ package {{invokerPackage}}.auth;
 
 import {{invokerPackage}}.Pair;
 
-import com.migcomponents.migbase64.Base64;
+import com.squareup.okhttp.Credentials;
 
 import java.util.Map;
 import java.util.List;
@@ -34,11 +34,8 @@ public class HttpBasicAuth implements Authentication {
     if (username == null && password == null) {
       return;
     }
-    String str = (username == null ? "" : username) + ":" + (password == null ? "" : password);
-    try {
-      headerParams.put("Authorization", "Basic " + Base64.encodeToString(str.getBytes("UTF-8"), false));
-    } catch (UnsupportedEncodingException e) {
-      throw new RuntimeException(e);
-    }
+    headerParams.put("Authorization", Credentials.basic(
+        username == null ? "" : username,
+        password == null ? "" : password));
   }
 }

modules/swagger-codegen/src/main/resources/Java/libraries/okhttp-gson/pom.mustache

@@ -122,11 +122,6 @@
       <artifactId>gson</artifactId>
       <version>${gson-version}</version>
     </dependency>
-    <dependency>
-      <groupId>com.brsanthu</groupId>
-      <artifactId>migbase64</artifactId>
-      <version>2.2</version>
-    </dependency>
 
     <!-- test dependencies -->
     <dependency>