Update kable_styling.R

add more escape values so feature will work correctly in latex.
diff --git a/R/kable_styling.R b/R/kable_styling.R
index cd996a8..40498e5 100644
--- a/R/kable_styling.R
+++ b/R/kable_styling.R
@@ -261,12 +261,12 @@
 
     if(table_info$tabular=="longtable") {
       out <- sub("\\\\begin\\{longtable\\}\\{l",
-                 paste0("\\begin\\{longtable\\}\\{",
+                 paste0("\\\\begin\\{longtable\\}\\{",
                         row_label_orientation),
                  out)
     } else {
       out <- sub("\\\\begin\\{tabular\\}\\{l",
-                 paste0("\\begin\\{tabular\\}\\{",
+                 paste0("\\\\begin\\{tabular\\}\\{",
                         row_label_orientation),
                  out)
     }