[Fix] nvm_ls: Reverts #1462 to fix io.js sorting.

<details>
<summary>Before this revert:</summary>

```sh
iojs-v3.3.1
iojs-v2.5.0
v0.6.21
v0.7.12
iojs-v1.8.4
v0.8.28
v0.9.12
v0.10.48
v0.11.16
v0.12.9
v0.12.18
v0.12.87
v4.9.1
v5.11.1
v5.12.0
v6.14.4
v6.16.0
v7.10.1
v8.6.0
v8.9.1
v8.10.0
v8.11.3
v8.11.4
v8.12.0
v8.13.0
v8.14.1
v8.15.0
v9.11.2
v10.0.0
v10.1.0
v10.2.1
v10.3.0
v10.4.1
v10.5.0
v10.6.0
v10.7.0
v10.8.0
v10.9.0
v10.10.0
v10.11.0
v10.12.0
v10.13.0
v10.14.2
v10.15.1
v11.0.0
v11.1.0
v11.2.0
v11.3.0
v11.4.0
v11.5.0
v11.6.0
v11.7.0
v11.8.0
v11.9.0
v11.10.0
```
</details>

<details>
<summary>After this revert:</summary>

```sh
v0.6.21
v0.7.12
v0.8.28
v0.9.12
v0.10.48
v0.11.16
v0.12.9
v0.12.18
v0.12.87
iojs-v1.8.4
iojs-v2.5.0
iojs-v3.3.1
v4.9.1
v5.11.1
v5.12.0
v6.14.4
v6.16.0
v7.10.1
v8.6.0
v8.9.1
v8.10.0
v8.11.3
v8.11.4
v8.12.0
v8.13.0
v8.14.1
v8.15.0
v9.11.2
v10.0.0
v10.1.0
v10.2.1
v10.3.0
v10.4.1
v10.5.0
v10.6.0
v10.7.0
v10.8.0
v10.9.0
v10.10.0
v10.11.0
v10.12.0
v10.13.0
v10.14.2
v10.15.1
v11.0.0
v11.1.0
v11.2.0
v11.3.0
v11.4.0
v11.5.0
v11.6.0
v11.7.0
v11.8.0
v11.9.0
v11.10.0
```
</details>

In other words, the sorting needs to happen *before* the `NVM_NODE_PREFIX` is removed.

nvm.sh

@@ -1082,9 +1082,9 @@ nvm_ls() {
             \\#${SEARCH_PATTERN}# !d;
           " \
           -e 's#^\([^/]\{1,\}\)/\(.*\)$#\2.\1#;' \
-          -e 's#\(.*\)\.\([^\.]\{1,\}\)$#\2-\1#;' \
-          -e "s#^${NVM_NODE_PREFIX}-##;" \
         | command sort -t. -u -k 1.2,1n -k 2,2n -k 3,3n \
+        | command sed -e 's#\(.*\)\.\([^\.]\{1,\}\)$#\2-\1#;' \
+                      -e "s#^${NVM_NODE_PREFIX}-##;" \
       )"
     fi
   fi

test/fast/Listing versions/Running "nvm ls" should display all installed versions.

@@ -25,3 +25,26 @@ nvm ls | grep v0.3.3 >/dev/null || die "v0.3.3 not found in: $(nvm ls)"
 nvm ls | grep v0.3.9 >/dev/null || die "v0.3.9 not found in: $(nvm ls)"
 nvm ls | grep v0.12.87 >/dev/null || die "v0.12.87 not found in: $(nvm ls)"
 nvm ls | grep iojs-v0.1.2 >/dev/null || die "iojs-v0.1.2 not found in: $(nvm ls)"
+
+OUTPUT="$(nvm_ls)"
+EXPECTED_OUTPUT="v0.0.1
+v0.0.2
+v0.0.3
+v0.0.9
+v0.0.20
+iojs-v0.1.2
+v0.1.3
+v0.1.4
+v0.2.3
+v0.3.1
+v0.3.3
+v0.3.9
+iojs-v0.10.2
+v0.12.9
+v0.12.87
+v0.20.3"
+if nvm_has_system_node || nvm_has_system_iojs; then
+  EXPECTED_OUTPUT="${EXPECTED_OUTPUT}
+system"
+fi
+[ "${OUTPUT-}" = "${EXPECTED_OUTPUT-}" ] || die "expected >${EXPECTED_OUTPUT}<; got >${OUTPUT}<"