Drop support for IntelliJ 2017

New features in 0.18 require IntelliJ 2018+.

Change-Id: Id872a921ab4a8eae70b217f9aca4ffda76b0ae1d
Reviewed-on: https://fuchsia-review.googlesource.com/c/intellij-language-fidl/+/628503
Reviewed-by: Alex Zaslavsky <azaslavsky@google.com>
diff --git a/resources/META-INF/plugin.xml b/resources/META-INF/plugin.xml
index b495af0..a35a2c8 100644
--- a/resources/META-INF/plugin.xml
+++ b/resources/META-INF/plugin.xml
@@ -127,7 +127,7 @@
   </change-notes>
 
   <!-- please see http://www.jetbrains.org/intellij/sdk/docs/basics/getting_started/build_number_ranges.html for description -->
-  <idea-version since-build="173.0"/>
+  <idea-version since-build="183.0"/>
 
   <!-- please see http://www.jetbrains.org/intellij/sdk/docs/basics/getting_started/plugin_compatibility.html
        on how to target different products -->