title: bokeh openStreetMap tile not visible in all browsers
body: <p>With the python bokeh (version 0.12.13) module i'm creating a .html with a line plotted on top of an openStreetMap tile (CARTODBPOSITRON):</p>
  
  <pre><code>from bokeh.models import ColumnDataSource
  from bokeh.plotting import figure
  from bokeh.tile_providers import CARTODBPOSITRON
  from bokeh.io import save,output_file
  
  #the data
  xList=[0.0, 111319, 222638, 333958, 445277, 556597, 667916, 779236, 890555]
  yList=[6446275, 5012341, 3763310, 2632018, 4163881, 5465442, 6800125, 6621293, 6446275]
  source=ColumnDataSource({'x':xList,'y':yList})
  
  x_range=(min(xList),max(xList))
  y_range=(min(yList),max(yList))
  plot = figure(title='printed line on map',tools= "pan,wheel_zoom",x_range=x_range,y_range=y_range,width=1200, height=400)#create a figure
  plot.add_tile(CARTODBPOSITRON)#add the CARTODBPOSITRON background tile
  
  #plot a dot an a line
  plot.line(source=source,x='x',y='y',line_color ='red')#line
  
  #save to html file
  output_file("file.html")
  save(plot)
  </code></pre>
  
  <p>The .html looks fine in my Chrome browser, but the map does not appear in my IE browser. When i shared the file with two friends, one of them also could not see the map in her Chrome browser. I've checked and un-checked the Chrome parameter "2D hardware acceleration", cleared cookies and so on but haven't found the solution there.</p>
  
  <p>Good (in my chrome browser, Version 66.0.3359.117 (Official Build) (32-bit), Windows 7, my friend her IE11):<a href="https://i.stack.imgur.com/JRydR.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/JRydR.png" alt="enter image description here"></a></p>
  
  <p>Bad (my IE11 (Version 11.0.9600.19002CO) browser, my friend her Chrome (also version 66.0.3359.117) browser):<a href="https://i.stack.imgur.com/6TIHT.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/6TIHT.png" alt="enter image description here"></a></p>
  
  <p>EDIT: For me it works in Chrome but not in IE11, for my friend it is opposite.</p>
  
  <p>This is a screenshot of the Network log from my IE11 (where it doesn't work):
  <a href="https://i.stack.imgur.com/xwhDD.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/xwhDD.png" alt="enter image description here"></a></p>
  
  <p>This is a screenshot of the Network log from my friend's Chrome (where it doesn't work):
  <a href="https://i.stack.imgur.com/8Vffb.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/8Vffb.png" alt="enter image description here"></a></p>