How to use a namespaced action in a Vue.js component

Component.vue

<template>
  <div>
    <button @click="increment">Increment</button>
  </div>
</template>

<script>
    import { mapActions } from 'vuex'
    export default{
      methods: {
            ...mapActions({
                'increment': 'namespace/actionMethod'
            })
      }
    }
</script>

I have problems using VUEX namespaced modules, I have an actions and mutation types files, How I am supposed to dispatch a module/action using a const name
export const FETCH_INSTITUCIONES = 'fetchInstituciones'
Before using namespaced modules I called

this.$store.dispatch(FETCH_INSTITUCIONES)

but it doesn´t work anymore, do you know how it's gotta be?