Correctly require composer plugin api version in test plugins

tests/Composer/Test/Plugin/Fixtures/plugin-v1/composer.json

@@ -5,5 +5,8 @@
     "autoload": { "psr-0": { "Installer": "" } },
     "extra": {
         "class": "Installer\\Plugin"
+    },
+    "require": {
+        "composer-plugin-api": "1.0.0"
     }
 }

tests/Composer/Test/Plugin/Fixtures/plugin-v2/composer.json

@@ -5,5 +5,8 @@
     "autoload": { "psr-0": { "Installer": "" } },
     "extra": {
         "class": "Installer\\Plugin2"
+    },
+    "require": {
+        "composer-plugin-api": "1.0.0"
     }
 }

tests/Composer/Test/Plugin/Fixtures/plugin-v3/composer.json

@@ -5,5 +5,8 @@
     "autoload": { "psr-0": { "Installer": "" } },
     "extra": {
         "class": "Installer\\Plugin2"
+    },
+    "require": {
+        "composer-plugin-api": "1.0.0"
     }
 }

tests/Composer/Test/Plugin/Fixtures/plugin-v4/composer.json

@@ -8,5 +8,8 @@
             "Installer\\Plugin1",
             "Installer\\Plugin2"
         ]
+    },
+    "require": {
+        "composer-plugin-api": "1.0.0"
     }
 }