Fix Gradle file usage

Gradle recommends to use the file DSL method instead of
directly opening files by Groovy/Java constructors
in build scripts.

build.gradle

@@ -68,7 +68,8 @@ configure(subprojects) {
             maven {
                 name = 'myLocalRepositoryForFullIntegrationTests'
                 //noinspection GrDeprecatedAPIUsage
-                url = new File(project.parent.buildDir, "maven-repo")
+                File baseDir = file(project.parent.buildDir)
+                url = new File (baseDir, "maven-repo")
             }
             mavenLocal()
         }
@@ -102,7 +103,8 @@ tasks.register("integrationTest") {
             commandLine "./gradlew", "clean", "htmlSanityCheck", "-PhtmlSanityCheckVersion=${project.version}"
         }
         logger.debug "Script output: $result"
-        final File testIndex = new File(INTEGRATION_TEST_DIRECTORY, "build/reports/index.html")
+        File integrationTestDirectory = file(INTEGRATION_TEST_DIRECTORY)
+        final File testIndex = new File (integrationTestDirectory, "build/reports/index.html")
         assert testIndex.exists()
     }
 }

integration-test/gradle-plugin/build.gradle

@@ -12,13 +12,13 @@ plugins {
 }
 
 htmlSanityCheck {
-    sourceDir = new File("src/test/resources")
+    sourceDir = file("src/test/resources")
 
     // where to put results of sanityChecks...
-    checkingResultsDir = new File("build/reports")
+    checkingResultsDir = file("build/reports")
 
-    logger.quiet "docToolchain> HSC sourceDir: ${sourceDir}"
-    logger.quiet "docToolchain> HSC checkingResultsDir: ${checkingResultsDir}"
+    logger.quiet "docToolchain> HSC sourceDir: ${sourceDir.absolutePath}"
+    logger.quiet "docToolchain> HSC checkingResultsDir: ${checkingResultsDir.absolutePath}"
 }
 
 tasks.register("clean", Delete) {