Updated Spring version.

backend/pom.xml

@@ -23,7 +23,7 @@
         <java.version>1.8</java.version>
         <kotlin.version>1.2.71</kotlin.version>
         <kotlin.compiler.jvmTarget>1.8</kotlin.compiler.jvmTarget>
-        <spring.version>2.0.5.RELEASE</spring.version>
+        <spring.version>2.0.6.RELEASE</spring.version>
     </properties>
 
     <dependencyManagement>
@@ -150,6 +150,7 @@
                     </execution>
                 </executions>
                 <groupId>org.jetbrains.kotlin</groupId>
+                <!--suppress DifferentMavenStdlibVersion -->
                 <version>${kotlin.version}</version>
                 <configuration>
                     <args>