BUGFIX: Avoid fatal error on PHP 7.3

Fixes #72

Author: kdambekalns

Classes/Suggestion/SuggestionContext.php

@@ -29,7 +29,7 @@ class SuggestionContext implements SuggestionContextInterface
      */
     protected $contextValues = [];
 
-    public function buildForIndex(NodeInterface $node): self
+    public function buildForIndex(NodeInterface $node): SuggestionContextInterface
     {
         $this->contextValues = [
             'siteName' => $this->getSiteName($node),
@@ -40,7 +40,7 @@ public function buildForIndex(NodeInterface $node): self
         return $this;
     }
 
-    public function buildForSearch(NodeInterface $node): self
+    public function buildForSearch(NodeInterface $node): SuggestionContextInterface
     {
         $this->contextValues = [
             'siteName' => $this->getSiteName($node),

Classes/Suggestion/SuggestionContextInterface.php

@@ -22,13 +22,13 @@ interface SuggestionContextInterface
      * Build the context from a given node
      * @param NodeInterface $node
      */
-    public function buildForIndex(NodeInterface $node): self;
+    public function buildForIndex(NodeInterface $node): SuggestionContextInterface;
 
     /**
      * Build the context from a given node
      * @param NodeInterface $node
      */
-    public function buildForSearch(NodeInterface $node): self;
+    public function buildForSearch(NodeInterface $node): SuggestionContextInterface;
 
     /**
      * Returns the calculated context identifier