Fixed incorrect emoji substitution

(cherry picked from commit 3d91734)

Author: GHTaarn

src/UnicodeREPL.jl

@@ -36,7 +36,7 @@ function substitution(istr::AbstractString)
                         "\\u(" * str
                     else
                         codepoint = m.match[1:end-1]
-                        Meta.parse("\"\\u$codepoint\"") * str[length(m.match)+1:end]
+                        Meta.parse("\"\\U$codepoint\"") * str[length(m.match)+1:end]
                     end
         end
         return ostr

test/substitution.jl

@@ -4,4 +4,5 @@ using UnicodeREPL
 @testset "substitution" begin
     @test UnicodeREPL.substitution("\\u(2560)\\u(2563)ello World!") == "╠╣ello World!"
     @test UnicodeREPL.substitution("\\u(bed) \\u(cab) \\u(feed) \\u(dad) \\u(BEEF)") == "௭ ಫ ﻭ ත 뻯"
+    @test UnicodeREPL.substitution("\\u(1F607) \\u(3b1)\\u(20E8)") == "😇 α⃨"
 end