Properly parse the target of a record update.

Fixes #796

Author: gdotdesign

spec/examples/record_update

@@ -106,3 +106,22 @@ component Main {
     ""
   }
 }
+-------------------------------------------------------------------------------
+type A {
+  b: B
+}
+
+type B {
+  str: String
+}
+
+component Main {
+  fun render {
+    let data = {b: {str: "text" }}
+
+    // let's create a copy updating only the "text"
+    let dataUpdated = { data | b: { data.b | str: "text2" } }
+
+    "ok"
+  }
+}

src/parsers/record_update.cr

@@ -6,7 +6,7 @@ module Mint
           next unless char! '{'
           whitespace
 
-          value = variable || self.expression
+          value = self.expression
           whitespace
 
           next unless value