Make code compatible with Ruby 2.7

Not including specs etc.

lib/nostr/errors/invalid_key_type_error.rb

@@ -13,6 +13,8 @@ module Nostr
     #
     # @param [String] key_kind The kind of key that is invalid (public or private)
     #
-    def initialize(key_kind) = super("Invalid #{key_kind} key type")
+    def initialize(key_kind)
+      super("Invalid #{key_kind} key type")
+    end
   end
 end

lib/nostr/key.rb

@@ -79,7 +79,9 @@ module Nostr
     #
     # @return [String] The bech32 string representation of the key
     #
-    def to_bech32 = Bech32.encode(hrp: self.class.hrp, data: self)
+    def to_bech32
+      Bech32.encode(hrp: self.class.hrp, data: self)
+    end
 
     protected
 

lib/nostr/keygen.rb

@@ -89,7 +89,7 @@ module Nostr
     def get_key_pair_from_private_key(private_key)
       validate_private_key(private_key)
       public_key = extract_public_key(private_key)
-      KeyPair.new(private_key:, public_key:)
+      KeyPair.new(private_key: private_key, public_key: public_key)
     end
 
     private

lib/nostr/user.rb

@@ -62,10 +62,10 @@ module Nostr
     )
       event = Event.new(
         pubkey: keypair.public_key,
-        kind:,
+        kind: kind,
-        content:,
+        content: content,
-        created_at:,
+        created_at: created_at,
-        tags:
+        tags: tags
       )
       event.sign(keypair.private_key)
     end