Fix parsing numeric literals with underscore in decimal part

The regexp adapted from Emacs' ada-mode was wrong,
and also not accept "E+..."

grammar.js

@@ -124,7 +124,7 @@ module.exports = grammar({
       character_literal: $ => token(/'.'/),
       numeric_literal: $ => token(
          choice(
-            /[0-9][0-9_]*(\.[0-9]+)?([eE][0-9_-]+)?/,
+            /[0-9][0-9_]*(\.[0-9_]+)?([eE][+-]?[0-9_]+)?/,
             /[0-9]+#[0-9a-fA-F._-]+#/
          )
       ),

src/grammar.json

@@ -50,7 +50,7 @@
         "members": [
           {
             "type": "PATTERN",
-            "value": "[0-9][0-9_]*(\\.[0-9]+)?([eE][0-9_-]+)?"
+            "value": "[0-9][0-9_]*(\\.[0-9_]+)?([eE][+-]?[0-9_]+)?"
           },
           {
             "type": "PATTERN",

test/corpus/literals.txt

@@ -4,7 +4,7 @@ String literals
 
 A : String := "12'34";
 
---------
+--------------------------------------------------------------------------------
 
 (compilation
   (compilation_unit
@@ -21,7 +21,7 @@ String literals with quotes
 
 A : String := "12""23";
 
---------
+--------------------------------------------------------------------------------
 
 (compilation
   (compilation_unit
@@ -32,3 +32,19 @@ A : String := "12""23";
         (term
           (string_literal))))))
 
+================================================================================
+Numeric literals with underscore
+================================================================================
+
+A : Integer := 12_14.12_122E+11_2;
+
+--------------------------------------------------------------------------------
+
+(compilation
+  (compilation_unit
+    (object_declaration
+      (identifier)
+      (identifier)
+      (expression
+        (term
+          (numeric_literal))))))