Merge pull request #35 from jarvist/master

Add check for Pluto.jl interactive notebook.

src/Gnuplot.jl

@@ -236,11 +236,12 @@ const sessions = OrderedDict{Symbol, Session}()
 const options = Options()
 
 function __init__()
-    # Check whether we are running in a IJulia or Juno session.
+    # Check whether we are running in an IJulia, Juno or Pluto session.
     # (copied from Gaston.jl).
     options.gpviewer = !(
         ((isdefined(Main, :IJulia)  &&  Main.IJulia.inited)  ||
-         (isdefined(Main, :Juno)    &&  Main.Juno.isactive()))
+         (isdefined(Main, :Juno)    &&  Main.Juno.isactive()) ||
+         (isdefined(Main, :PlutoRunner)) )
     )
 end