Update PLUGIN_DEV.md (#19387)

Minor edits, removed a broken link. It led to a 404 page.

PLUGIN_DEV.md

-# Plugin Development 
+# Plugin development 
 
 This document is not meant as a complete guide for developing plugins but more as a changelog for changes in
 Grafana that can impact plugin development. Whenever you as a plugin author encounter an issue with your plugin after
 upgrading Grafana please check here before creating an issue. 
 
-## Links
+## Plugin development resources
 
-- [Datasource plugin written in TypeScript](https://github.com/grafana/typescript-template-datasource)
-- [Simple JSON datasource plugin](https://github.com/grafana/simple-json-datasource)
-- [Plugin development guide](http://docs.grafana.org/plugins/developing/development/)
+- [Grafana plugin developer guide](http://docs.grafana.org/plugins/developing/development/)
 - [Webpack Grafana plugin template project](https://github.com/CorpGlory/grafana-plugin-template-webpack)
+- [Simple JSON datasource plugin](https://github.com/grafana/simple-json-datasource)
 
-## Changes in v4.6
+## Changes in Grafana v4.6
 
 This version of Grafana has big changes that will impact a limited set of plugins. We moved from systemjs to webpack
-for built-in plugins & everything internal. External plugins still use systemjs but now with a limited 
+for built-in plugins and everything internal. External plugins still use systemjs but now with a limited 
 set of Grafana components they can import. Plugins can depend on libs like lodash & moment and internal components 
 like before using the same import paths. However since everything in Grafana is no longer accessible, a few plugins could encounter issues when importing a Grafana dependency. 
 
@@ -25,10 +24,10 @@ If you think we missed exposing a crucial lib or Grafana component let us know b
 ### Deprecated components 
 
 The angular directive `<spectrum-picker>` is now deprecated (will still work for a version more) but we recommend plugin authors
-to upgrade to new `<color-picker color="ctrl.color" onChange="ctrl.onSparklineColorChange"></color-picker>`
+upgrade to new `<color-picker color="ctrl.color" onChange="ctrl.onSparklineColorChange"></color-picker>`
 
-## Changes in v6.0
+## Changes in Grafana v6.0
 
 ### DashboardSrv.ts
 
-If you utilize [DashboardSrv](https://github.com/grafana/grafana/commit/8574dca081002f36e482b572517d8f05fd44453f#diff-1ab99561f9f6a10e1fafcddc39bc1d65) in your plugin code, `dash` was renamed to `dashboard` 
+If you utilize [DashboardSrv](https://github.com/grafana/grafana/commit/8574dca081002f36e482b572517d8f05fd44453f#diff-1ab99561f9f6a10e1fafcddc39bc1d65) in your plugin code, `dash` was renamed to `dashboard`.