remove gradleApi() usage because of GRADLE-1715 / GRADLE-2516 problems

- see http://forums.gradle.org/gradle/topics/gradle_doesnt_allow_me_to_override_snakeyaml_1_6_to_snakeyaml_1_10 for details

Author: lhotari

grails-shell/build.gradle

@@ -6,6 +6,10 @@ repositories {
     jcenter()
 }
 
+ext {
+    gradleToolingApiVersion = gradle.gradleVersion
+}
+
 dependencies {
     compile project(":grails-bootstrap")
     compile "org.apache.ant:ant:$antVersion"
@@ -14,7 +18,7 @@ dependencies {
     compile "org.fusesource.jansi:jansi:$jansiVersion"
     compile "jline:jline:$jlineVersion"
     compile "org.eclipse.jgit:org.eclipse.jgit:3.5.2.201411120430-r"
-    compile gradleApi()
+    compile "org.gradle:gradle-tooling-api:$gradleToolingApiVersion"
 
     compile("org.springframework.boot:spring-boot-cli:$springBootVersion")