Merge pull request #111 from pzygielo/recognize_url_env_var

usage of MVNW_REPOURL for wrapper download
diff --git a/mvnw b/mvnw
index eb65ff2..b17728f 100755
--- a/mvnw
+++ b/mvnw
@@ -211,7 +211,7 @@
     if [ "$MVNW_VERBOSE" = true ]; then
       echo "Couldn't find .mvn/wrapper/maven-wrapper.jar, downloading it ..."
     fi
-    if [ "$MVNW_REPOURL" = true]; then
+    if [ -n "$MVNW_REPOURL" ]; then
       jarUrl="$MVNW_REPOURL/io/takari/maven-wrapper/0.5.2/maven-wrapper-0.5.2.jar"
     else
       jarUrl="https://repo.maven.apache.org/maven2/io/takari/maven-wrapper/0.5.2/maven-wrapper-0.5.2.jar"