Fixed debug mode in gradle plugin (#546)

### What's done:
* Hotfix for gradle plugin
* Updated pom.xml
* Updated README.md
* Updated metrics_for_master.yml

Author: petertrr

.github/workflows/metrics_for_master.yml

@@ -25,7 +25,7 @@ jobs:
           restore-keys: |
             ${{ runner.os }}-maven-build-
       - name: Run tests
-        run: mvn -B test
+        run: mvn -B test -DskipPluginMarker
       - name: Generate code coverage report
         uses: codecov/codecov-action@v1
         with:

diktat-gradle-plugin/README.md

@@ -6,7 +6,4 @@ To avoid versions duplication, diktat and ktlint versions are passed to gradle v
 These versions are then written in a file and then included in the plugin jar to determine dependencies for JavaExec.
 
 Gradle plugin marker pom, which is normally produced by `java-gradle-plugin` plugin during gradle build,
-is added manually as a maven module.
-
-Build is skipped by default on windows to make things easier; if you want to build it, you should change
-the property `gradle.executable` to `gradlew.bat` and the property `skip.gradle.build` to `true`.
+is added manually as a maven module.

diktat-gradle-plugin/gradle-plugin-marker/pom.xml

@@ -11,7 +11,6 @@
     <groupId>org.cqfn.diktat.diktat-gradle-plugin</groupId>
     <artifactId>org.cqfn.diktat.diktat-gradle-plugin.gradle.plugin</artifactId>
     <packaging>pom</packaging>
-    <version>0.1.5-SNAPSHOT</version>
 
     <dependencies>
         <dependency>

diktat-gradle-plugin/pom.xml

@@ -161,7 +161,7 @@
                 </os>
             </activation>
             <properties>
-                <skip.gradle.build>true</skip.gradle.build>
+                <gradle.executable>${project.basedir}/gradlew.bat</gradle.executable>
             </properties>
         </profile>
     </profiles>

diktat-gradle-plugin/src/main/kotlin/org/cqfn/diktat/plugin/gradle/DiktatJavaExecTaskBase.kt

@@ -42,7 +42,9 @@ open class DiktatJavaExecTaskBase @Inject constructor(
             logger.lifecycle("Running diktat $DIKTAT_VERSION with ktlint $KTLINT_VERSION")
         }
         args = additionalFlags.toMutableList().apply {
-            add(if (diktatExtension.debug) "--debug" else "")
+            if (diktatExtension.debug) {
+                add("--debug")
+            }
             add(diktatExtension.inputs.files.joinToString { it.path })
         }
     }