raw cell placeholder text as one line

IPython/html/static/notebook/js/textcell.js

@@ -376,8 +376,8 b' var IPython = (function (IPython) {'
     };
 
     RawCell.options_default = {
-        placeholder : "Write raw LaTeX or other formats here, for use with nbconvert.\n" +
-            "It will not be rendered in the notebook.\n" + 
+        placeholder : "Write raw LaTeX or other formats here, for use with nbconvert. " +
+            "It will not be rendered in the notebook. " + 
             "When passing through nbconvert, a Raw Cell's content is added to the output unmodified."
     };