min-width instead of width for prompt

mainly helpfull for nbviewer responsive css to have the prompt
above the code cells, and have the correct width.

IPython/html/static/notebook/less/cell.less

@@ -15,7 +15,7 @@ div.cell {
 
 div.prompt {
     /* This needs to be wide enough for 3 digit prompt numbers: In[100]: */
-    width: 11ex;
+    min-width: 11ex;
     /* This 0.4em is tuned to match the padding on the CodeMirror editor. */
     padding: 0.4em;
     margin: 0px;

IPython/html/static/style/ipython.min.css

@@ -55,7 +55,7 @@ input.engine_num_input{height:20px;margin-bottom:2px;padding-top:0;padding-botto
 .ansibgcyan{background-color:cyan;}
 .ansibggray{background-color:gray;}
 div.cell{border:1px solid transparent;display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;width:100%;padding:5px 5px 5px 0px;margin:2px 0px 2px 7px;outline:none;}div.cell.selected{border-radius:4px;border:thin #ababab solid;}
-div.prompt{width:11ex;padding:0.4em;margin:0px;font-family:monospace;text-align:right;line-height:1.231em;}
+div.prompt{min-width:11ex;padding:0.4em;margin:0px;font-family:monospace;text-align:right;line-height:1.231em;}
 div.input{page-break-inside:avoid;display:-webkit-box;-webkit-box-orient:horizontal;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:horizontal;-moz-box-align:stretch;display:box;box-orient:horizontal;box-align:stretch;}
 div.input_area{border:1px solid #cfcfcf;border-radius:4px;background:#f7f7f7;}
 div.input_prompt{color:navy;border-top:1px solid transparent;}

IPython/html/static/style/style.min.css

@@ -1436,7 +1436,7 @@ input.engine_num_input{height:20px;margin-bottom:2px;padding-top:0;padding-botto
 .ansibgcyan{background-color:cyan;}
 .ansibggray{background-color:gray;}
 div.cell{border:1px solid transparent;display:-webkit-box;-webkit-box-orient:vertical;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:vertical;-moz-box-align:stretch;display:box;box-orient:vertical;box-align:stretch;width:100%;padding:5px 5px 5px 0px;margin:2px 0px 2px 7px;outline:none;}div.cell.selected{border-radius:4px;border:thin #ababab solid;}
-div.prompt{width:11ex;padding:0.4em;margin:0px;font-family:monospace;text-align:right;line-height:1.231em;}
+div.prompt{min-width:11ex;padding:0.4em;margin:0px;font-family:monospace;text-align:right;line-height:1.231em;}
 div.input{page-break-inside:avoid;display:-webkit-box;-webkit-box-orient:horizontal;-webkit-box-align:stretch;display:-moz-box;-moz-box-orient:horizontal;-moz-box-align:stretch;display:box;box-orient:horizontal;box-align:stretch;}
 div.input_area{border:1px solid #cfcfcf;border-radius:4px;background:#f7f7f7;}
 div.input_prompt{color:navy;border-top:1px solid transparent;}