Update release notes

Author: kMutagene

src/Plotly.NET.ImageExport/RELEASE_NOTES.md

@@ -1,3 +1,5 @@
-### 3.0.0 - June 10 2020
+### 3.0.0 - June 15 2020
 
-Test
+This release adopts strong assembly naming. 
+This might cause backwards incompatibility and therefore results in an early major version increase. 
+For more insights why we do this, check out the conversation on this [issue](https://github.com/plotly/Plotly.NET/issues/175)

src/Plotly.NET.Interactive/RELEASE_NOTES.md

@@ -1,3 +1,5 @@
-### 3.0.0 - June 10 2020
+### 3.0.0 - June 15 2020
 
-Test
+This release adopts strong assembly naming. 
+This might cause backwards incompatibility and therefore results in an early major version increase. 
+For more insights why we do this, check out the conversation on this [issue](https://github.com/plotly/Plotly.NET/issues/175)

src/Plotly.NET/RELEASE_NOTES.md

@@ -1,3 +1,9 @@
-### 3.0.0 - June 10 2020
+### 3.0.0 - June 15 2020
 
-Test
+This release adopts strong assembly naming. 
+This might cause backwards incompatibility and therefore results in an early major version increase. 
+For more insights why we do this, check out the conversation on this [issue](https://github.com/plotly/Plotly.NET/issues/175)
+
+Other additions:
+
+- [fix legend xanchor plotly attribute name](https://github.com/plotly/Plotly.NET/commit/0d612f9c847609c8f676ade0acfada11f137d833) ([#289](https://github.com/plotly/Plotly.NET/issues/289))