Updated cell style references

IPython/nbconvert/templates/latex/latex_article.tplx

@@ -1,7 +1,7 b''
 
 % Default to the notebook output style
 ((* if not cell_style is defined *))
-    ((* set cell_style = 'ipython_style.tplx' *))
+    ((* set cell_style = 'style_bw_ipython.tplx' *))
 ((* endif *))
 
 % Inherit from the specified cell style.

IPython/nbconvert/templates/latex/latex_report.tplx

@@ -1,7 +1,7 b''
 
 % Default to the notebook output style
 ((* if not cell_style is defined *))
-    ((* set cell_style = 'ipython_style.tplx' *))
+    ((* set cell_style = 'style_ipython.tplx' *))
 ((* endif *))
 
 % Inherit from the specified cell style.