Closes Viz page #39. removes ggplot2 refs

Author: aeturrell

data-visualise.ipynb

@@ -1089,7 +1089,7 @@
    "source": [
     "## Summary\n",
     "\n",
-    "In this chapter, you've learned the basics of data visualisation with ggplot2.\n",
+    "In this chapter, you've learned the basics of data visualisation with **letsplot**.\n",
     "We started with the basic idea that underpins **letsplot**: a visualisation is a mapping from variables in your data to aesthetic properties like position, colour, size and shape.\n",
     "You then learned about increasing the complexity and improving the presentation of your plots layer-by-layer.\n",
     "You also learned about commonly used plots for visualising the distribution of a single variable as well as for visualising relationships between two or more variables, by leveraging additional aesthetic mappings and/or splitting your plot into small multiples using faceting.\n",

vis-layers.ipynb

@@ -860,7 +860,8 @@
    "metadata": {},
    "source": [
     "Adding randomness seems like a strange way to improve your plot, but while it makes your graph less accurate at small scales, it makes your graph *more* revealing at large scales.\n",
-    "Because this is such a useful operation, ggplot2 comes with a shorthand for `geom_point(position = \"jitter\")`: `geom_jitter()`.\n",
+    "\n",
+    "Because this is such a useful operation, **letsplot** comes with a shorthand for `geom_point(position = \"jitter\")`: `geom_jitter()`.\n",
     "\n",
     "Of course, a more sophisticated way of dealing with overplotting is via a binscatter plot, which is available in the [**binsreg**](https://nppackages.github.io/binsreg/) package.\n",
     "\n",