fixed code view line height for firefox

public/ng/css/gogs.css

@@ -1416,7 +1416,7 @@ The register and sign-in page style
 }
 .code-view .lines-num span {
   font-family: Monaco, Menlo, Consolas, "Courier New", monospace;
-  line-height: 1.6;
+  line-height: 20px;
   padding: 0 10px;
   cursor: pointer;
   display: block;

public/ng/less/gogs/repository.less

@@ -447,7 +447,7 @@
         width: 1%;
         span {
             font-family: Monaco,Menlo,Consolas,"Courier New",monospace;
-            line-height: 1.6;
+            line-height: 20px;
             padding: 0 10px;  
             cursor: pointer;
             display: block;