Ensure correct path to javac

Author: keynmol

src/main/scala/com/sourcegraph/sbtsourcegraph/Versions.scala

@@ -79,10 +79,16 @@ object Versions {
             case Some(javaHome) =>
               val sb = new StringBuilder
               val proc = {
+                val cmd =
+                  if (scala.util.Properties.isWin)
+                    Paths.get("bin", "javac.exe")
+                  else Paths.get("bin", "javac")
+
                 val stdout = scala.sys.process
-                  .Process(Seq("javac", "-version"), cwd = javaHome)
+                  .Process(Seq(cmd.toString(), "-version"), cwd = javaHome)
                   .!!(ProcessLogger(sb.append(_)))
                   .trim
+
                 // Java 8 sends output to stderr...
                 if (stdout.isEmpty()) sb.result().trim else stdout
               }