Add Second Ouguiya MRU 929 to currency iso file (#853)

* Add Second Ouguiya MRU 929 to currency iso file

* Remove currency MRO (has been superseded by MRU)

The first Mauritanian Ouguiya (currency code MRO, ISO code 478) has been
replaced by the second Ouguiya (currency code MRU, ISO code 929) on
January 01, 2018. Fore more informatiom, see the following links:

    https://en.wikipedia.org/wiki/ISO_4217
    https://en.wikipedia.org/wiki/Mauritanian_ouguiya

* Fix unit tests after replacing MRO by MRU

* Make sure deprecated currency MRO is not mentioned anywhere in the code

* Fix unit tests

* Add MRO to currency_backwards_compatible.json

The disambiguate symbol "A-UM" has been added for MRO, see

    https://www.bcm.mr/IMG/pdf/directives_techniques.pdf

config/currency_backwards_compatible.json

@@ -60,6 +60,22 @@
     "iso_numeric": "428",
     "smallest_denomination": 1
   },
+  "mro": {
+    "priority": 100,
+    "iso_code": "MRO",
+    "name": "Mauritanian Ouguiya",
+    "symbol": "UM",
+    "disambiguate_symbol": "A-UM",
+    "alternate_symbols": [],
+    "subunit": "Khoums",
+    "subunit_to_unit": 5,
+    "symbol_first": false,
+    "html_entity": "",
+    "decimal_mark": ".",
+    "thousands_separator": ",",
+    "iso_numeric": "478",
+    "smallest_denomination": 1
+  },
   "mtl": {
     "priority": 100,
     "iso_code": "MTL",

config/currency_iso.json

@@ -1412,9 +1412,9 @@
     "iso_numeric": "446",
     "smallest_denomination": 10
   },
-  "mro": {
+  "mru": {
     "priority": 100,
-    "iso_code": "MRO",
+    "iso_code": "MRU",
     "name": "Mauritanian Ouguiya",
     "symbol": "UM",
     "alternate_symbols": [],
@@ -1424,7 +1424,7 @@
     "html_entity": "",
     "decimal_mark": ".",
     "thousands_separator": ",",
-    "iso_numeric": "478",
+    "iso_numeric": "929",
     "smallest_denomination": 1
   },
   "mur": {

lib/money/currency.rb

@@ -414,7 +414,7 @@ def iso?
 
     # Returns the relation between subunit and unit as a base 10 exponent.
     #
-    # Note that MGA and MRO are exceptions and are rounded to 1
+    # Note that MGA and MRU are exceptions and are rounded to 1
     # @see https://en.wikipedia.org/wiki/ISO_4217#Active_codes
     #
     # @return [Integer]

spec/currency_spec.rb

@@ -385,7 +385,7 @@ def to_s
 
   describe "#decimal_places" do
     it "proper places for known currency" do
-      expect(described_class.new(:mro).decimal_places).to eq 1
+      expect(described_class.new(:mru).decimal_places).to eq 1
       expect(described_class.new(:usd).decimal_places).to eq 2
     end